This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A340491 #20 Feb 20 2021 00:32:05 %S A340491 3,6,9,11,10,7,7,1,1 %N A340491 Number of n-digit numbers x such that rev(x^2) = rev(x)^2 and x does not contain any zero digits, where rev(x) is the digit reversal of x. %C A340491 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. %e A340491 The 7 solutions with 7 digits are 1111111, 1111112, 1111121, 1111211, 1121111, 1211111, 2111111. %o A340491 (PARI) isok(k) = my(d=digits(k)); vecmin(d) && (fromdigits(Vecrev(digits(k^2))) == fromdigits(Vecrev(d))^2); %o A340491 a(n) = sum(k=10^(n-1), 10^n-1, isok(k)); \\ _Michel Marcus_, Jan 16 2021 %Y A340491 Cf. A098701 (number of solutions) and A085305 (the solutions), where digit 0 is not forbidden. %Y A340491 Cf. A004086 (digit reversal), A052382 (zeroless numbers). %K A340491 nonn,base,fini,full %O A340491 1,1 %A A340491 _Sébastien Dumortier_, Jan 10 2021