This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A273359 Numbers n such that the decimal number concat(4,n) is a square. 8
 9, 41, 84, 225, 356, 489, 624, 761, 900, 1209, 1616, 2025, 2436, 2849, 3264, 3681, 4100, 4521, 4944, 5369, 5796, 6225, 6656, 7089, 7524, 7961, 8400, 8841, 9284, 9729, 10881, 12164, 13449, 14736, 16025, 17316, 18609, 19904, 21201, 22500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Elements are squares of integers in (sqrt(41), sqrt(50)) * sqrt(10)^k without the leading 4 elements for nonnegative k. - David A. Corneth, May 20 2016 LINKS Nathan Fox, Table of n, a(n) for n = 1..10000 EXAMPLE 84 is a member because 484 = 22^2 is a square. 0 is not a member because 40 is not a square. sqrt(410) < 21 AND 22 < sqrt(500) < 23 so 21^2 = 441 and 22^2 = 484 give 41 and 84 respectively. 64 < sqrt(4100) < 65 AND 70 < sqrt(5000) < 71 so 65^2 = 4225, 66^2 = 4356, ..., 70^2 = 4900 give 225, 356, ..., 900 respectively. - David A. Corneth, May 20 2016 MAPLE t1:=[]; for k from 1 to 30000 do if issqr(k+4*10^length(k)) then t1:=[op(t1), k]; fi; od; t1; PROG a(n) = {my(k=1, t=0); while(n>k, n-=k; t++; k=floor(sqrt(50)*sqrt(10^t))- ceil(sqrt(41)*sqrt(10^t))+1); (ceil(sqrt(41)*sqrt(10^t))+n-1)^2%(40*10^t)} \\ David A. Corneth, May 20 2016 CROSSREFS Cf. A272671, A273357, A273358, A273360, A273361, A273362, A273363, A273364 Sequence in context: A000451 A000437 A095809 * A251422 A018836 A245932 Adjacent sequences:  A273356 A273357 A273358 * A273360 A273361 A273362 KEYWORD nonn,base AUTHOR Nathan Fox, Brooke Logan, and N. J. A. Sloane, May 20 2016 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 October 18 12:18 EDT 2019. Contains 328160 sequences. (Running on oeis4.)