April Fools Day!

Question

Your challenge is simple: write a program or function which appears to print the first ten numbers of any integer sequence (on OEIS, the answerer may choose which sequence), but instead prints the exact text:

Happy April Fool's Day!

if and only if it is run on April 1st of any year. Run on any other day should make it output its original output. (Unfortunately, I was a little late posting this challenge). Answers should be voted up for clever hiding of the April fools part.

This is a popularity-contest, so the answer with the most votes on May 8th wins!

Answer 1

TI-Basic (TI-84 Plus CE)

{1001,10,1}→LA
{1010,1,1}→LA
{1011,11,1}→LB
{1020,2,1}→LC
{1021,12,1}→LD
{1030,3,1}→LE
{1040,4,1}→LF
{1050,5,1}→LG
{1060,6,1}→LH
{1070,7,1}→LI

getDate→L1

IF L1(2)=LA(2) and L1(3)=LA(3):Then
"Happy October First!"
End
IF L1(2)=LB(2) and L1(3)=LB(3):Then
"Happy New Year!"
End
IF L1(2)=LC(2) and L1(3)=LC(3):Then
"Happy November First!"
End
IF L1(2)=LD(2) and L1(3)=LD(3):Then
"Happy February First!"
End
IF L1(2)=LE(2) and L1(3)=LE(3):Then
"Happy December First!"
End
IF L1(2)=LF(2) and L1(3)=LF(3):Then
"Happy March First!"
End
IF L1(2)=LG(2) and L1(3)=LG(3):Then
Disp "Happy April Fool's Day!"
Return:End
IF L1(2)=LH(2) and L1(3)=LH(3):Then
"Happy May First!"
End
IF L1(2)=LI(2) and L1(3)=LI(3):Then
"Happy June First!"
End
IF L1(2)=LJ(2) and L1(3)=LJ(3):Then
"Happy July First!"
End

ClrHome
Output(1,1,toString(10000LA(1)+100LA(2)+LA(3)))
Output(2,1,toString(10000LB(1)+100LB(2)+LB(3)))
Output(3,1,toString(10000LC(1)+100LC(2)+LC(3)))
Output(4,1,toString(10000LD(1)+100LD(2)+LD(3)))
Output(5,1,toString(10000LE(1)+100LE(2)+LE(3)))
Output(6,1,toString(10000LF(1)+100LF(2)+LF(3)))
Output(7,1,toString(10000LG(1)+100LG(2)+LG(3)))
Output(8,1,toString(10000LH(1)+100LH(2)+LH(3)))
Output(9,1,toString(10000LI(1)+100LI(2)+LI(3)))
Output(10,1,toString(10000LJ(1)+100LJ(2)+LJ(3)))

Uses OEIS A210884.

Stores the numbers as dates and converts them on-the-fly to output. It even leaves you a message in Ans if today is one of the dates!

Answer 2

C

I use some fun CLANG properties to do tricky math and print the text sneakishly. I am printing the sequence of even numbers 0,2,4,6 etc up to 42.

This is a nice solution because I don't use any letters or hard coded strings, just pure math trickery to end up outputting the desired text even though it appears to a human brain that this should just be outputting 0,2,4,6,etc

Try it online! (Just the sneaky April Fools Day version)

#define printNumber(x) printf("%c", x)

main() {

    SYSTEMTIME st;
    GetLocalTime(&st);
    BOOL isFunDay = (st.wDay == 4 && st.wDay == 1);

    if (isFunDay) {
        printEvenNumbersTheFunWay();//fun way for a fun day!
    } else {
        printSomeEvenNumbersTheBoringWay();
    }

}

printEvenNumbersTheFunWay() {

    //print sequence: 0,2,4,6,8,10,12,14...42

    //print 0
    #define zero 72-72
    printNumber(2*zero+0);

    //print 2
    #define zero 5-5
    printNumber(20*zero+2);

    //print 4
    #define zero 108-108
    printNumber(2*zero+4);

    //print 6
    #define zero 106-106
    printNumber(2*zero+6);

    //print 8
    #define zero 113-113
    printNumber(2*zero+8);

    //print 10
    #define zero 22-22
    printNumber(2*zero+10);

    //print 12
    #define zero 53-53
    printNumber(2*zero+12);

    //print 14
    #define zero 98-98
    printNumber(2*zero+14);

    //print 16
    #define zero 98-98
    printNumber(2*zero+16);

    //print 18
    #define zero 87-87
    printNumber(2*zero+18);

    //print 20
    #define zero 88-88
    printNumber(2*zero+20);

    //print 22
    #define zero 10-10
    printNumber(2*zero+22);

    //print 24
    #define zero 46-46
    printNumber(2*zero+24);

    //print 26
    #define zero 85-85
    printNumber(2*zero+26);

    //print 28
    #define zero 83-83
    printNumber(2*zero+28);

    //print 30
    #define zero 78-78
    printNumber(2*zero+30);

    //print 32
    #define zero 7-7
    printNumber(2*zero+32);

    //print 34
    #define zero 81-81
    printNumber(2*zero+34);

    //print 36
    #define zero 2-2
    printNumber(-1*zero+36);

    //print 38
    #define zero 30-30
    printNumber(2*zero+38);

    //print 40
    #define zero 57-57
    printNumber(2*zero+40);

    //print 42
    #define zero 79-79
    printNumber(2*zero+42);

    //print 44
    #define zero 1-1
    printNumber(-10*zero+44);

}

printSomeEvenNumbersTheBoringWay() {

    //print sequence: 0,2,4,6,8,10,12,14...42

    int i = 0;
    while (i <= 42) {
        printf("%i, ", i);
        i+=2;
    }

}

Answer 3

JS, A000027

d=new Date();
if(d.getMonth()+("")[(![]+"")[+[]]+"ontcol"+(!![]+[]["fi"+(![]+"")[!+[]+!+[]]+"l"])[10]+"r"]()[11]+("")["fon"+(!![]+"")[0]+"color"]()[11]+!+[]+!+[]*!+[]+!+[]&&d.getDate()==+!+[])alert("Happy April Fool's Day!");
else{for(i=0;i<10;)alert(++i);}

Mmm, good mixture of JS and JSF*ck. (Fun fact: The majority of the code is used to represent ==.)

Good tip for corrupting code like mine: JS to JSFuck Conversion code/list

Answer 4

Python 2, A000027

import datetime as a
if(str(a.date.today())[5:]=='04-01'):print("Happy April Fool's Day!")
else:
 for i in range(10):print(i+1)

Try it online!