A221651 Numbers divisible by their first digit squared (excluding those whose first digit is 1).
20, 24, 28, 36, 48, 50, 200, 204, 208, 212, 216, 220, 224, 228, 232, 236, 240, 244, 248, 252, 256, 260, 264, 268, 272, 276, 280, 284, 288, 292, 296, 306, 315, 324, 333, 342, 351, 360, 369, 378, 387, 396, 400, 416, 432, 448, 464, 480, 496, 500, 525, 550, 575
Offset: 1
Examples
48 is divisible by 4^2.
Links
- Christian N. K. Anderson, Table of n, a(n) for n = 1..10000
- Christian N. K. Anderson, Ulam Spiral for the first 10000 terms. [Draw the usual Ulam spiral, containing all the nonnegative integers, and color the numbers belonging to this sequence yellow]
Programs
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R
x=0; y=rep(0,1000); len=0 firstdig<-function(x) as.numeric(substr(as.character(x),1,1)) isint<-function(x) x==as.integer(x) while(len<10000) if((fd=firstdig((x=x+1)))>1) if(isint(x/fd^2)) y[(len=len+1)]=x
Comments