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 A263620 #24 Jun 15 2024 01:02:25
%S A263620 3,6,14,19,30,36,55,69,94,112,161,192,263,309,414,485,639,740,949,
%T A263620 1081,1373,1555
%N A263620 Number of nonzero palindromic squares with at most 2n digits.
%H A263620 G. J. Simmons, <a href="/A002778/a002778_2.pdf">Palindromic powers</a>, J. Rec. Math., 3 (No. 2, 1970), 93-98. [Annotated scanned copy] See page 95.
%F A263620 Equals A263619(2n)-1.
%t A263620 Table[Length[Select[Range[1, Floor[Sqrt[10^(2 n)]]], PalindromeQ[#^2] &]], {n, 6}] (* _Robert Price_, Apr 26 2019 *)
%o A263620 (Python)
%o A263620 def ispal(n): s = str(n); return s == s[::-1]
%o A263620 def a(n):
%o A263620 c, k, kk = 0, 1, 1
%o A263620 while kk < 10**(2*n): c, k, kk = c + (ispal(kk)), k+1, kk + 2*k + 1
%o A263620 return c
%o A263620 print([a(n) for n in range(1, 8)]) # _Michael S. Branicky_, Mar 06 2021
%Y A263620 Cf. A002778, A002779, A263617, A263617, A263618, A263619.
%K A263620 nonn,base,more
%O A263620 1,1
%A A263620 _N. J. A. Sloane_, Oct 23 2015
%E A263620 a(7)-a(10) from _Chai Wah Wu_, Oct 25 2015
%E A263620 More terms using A263618 from _Chai Wah Wu_, Jun 14 2024