The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A221651 Numbers divisible by their first digit squared (excluding those whose first digit is 1). 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers where  floor(n/10^floor(log(n)))^2 divides n. 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] EXAMPLE 48 is divisible by 4^2. PROG (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 CROSSREFS Cf. A132359, A034709, A034837, A005349, A007602, A034838, A225297, A225722, A225683. Sequence in context: A250289 A114843 A174629 * A108373 A109131 A171696 Adjacent sequences:  A221648 A221649 A221650 * A221652 A221653 A221654 KEYWORD nonn,base AUTHOR Kevin L. Schwartz and Christian N. K. Anderson, May 04 2013 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 2 05:01 EST 2021. Contains 349437 sequences. (Running on oeis4.)