A098690 Number of solutions to rev(x^2)=rev(x)^2 below 10^n.

3, 9, 24, 63, 153, 362, 819, 1810, 3872, 8160, 16681, 33756, 66864, 130937, 251982, 480793, 903981, 1685563, 3106008, 5677863, 10276935, 18464658, 32891187, 58169964, 102136772, 178096364, 308593319, 531191384, 909227946, 1546356485, 2617639292

Offset

1,1

Comments

Partial sums of A098701. - Michel Marcus, Apr 11 2014

Excludes multiples of 10. - David Radcliffe, Aug 28 2021

Also the number of skinny numbers (A061909) with n digits, excluding 0. - David Radcliffe, Aug 28 2021

Links

Table of n, a(n) for n=1..31.

Example

For n = 2 the a(2) = 9 solutions are 1, 2, 3, 11, 12, 13, 21, 22, 31. - David Radcliffe, Aug 28 2021

Mathematica

f[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Differences[Table[Length[Select[Range[10^n], f[#^2]==f[#]^2&]], {n, 0, 6}]] (* Geoffrey Critzer, Dec 18 2013 *)

Prog

(Python)
def rev(n): return int(str(n)[::-1])
def a(n): return sum(k % 10 and rev(k**2) == rev(k)**2 for k in range(10**n)) # David Radcliffe, Aug 28 2021

Crossrefs

Cf. A085305, A225301.

Sequence in context: A342795 A267465 A018788 * A267960 A268938 A090400

Adjacent sequences: A098687 A098688 A098689 * A098691 A098692 A098693

Keyword

nonn,base

Author

Martin Renner, Oct 27 2004

Extensions

a(7),a(8) from Geoffrey Critzer, Dec 18 2013

Extended using A098701 by Michel Marcus, Apr 11 2014

Status

approved