OFFSET
1,1
COMMENTS
The number of solutions of rev(x^2) = rev(x)^2 increases but the solutions with a 0 don't. Any number with more than 9 digits can't be a solution, due to the development of x^2.
EXAMPLE
The 7 solutions with 7 digits are 1111111, 1111112, 1111121, 1111211, 1121111, 1211111, 2111111.
PROG
(PARI) isok(k) = my(d=digits(k)); vecmin(d) && (fromdigits(Vecrev(digits(k^2))) == fromdigits(Vecrev(d))^2);
a(n) = sum(k=10^(n-1), 10^n-1, isok(k)); \\ Michel Marcus, Jan 16 2021
CROSSREFS
KEYWORD
nonn,base,fini,full
AUTHOR
Sébastien Dumortier, Jan 10 2021
STATUS
approved