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
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
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