

A263620


Number of nonzero palindromic squares with at most 2n digits.


3




OFFSET

1,1


LINKS

Table of n, a(n) for n=1..10.
G. J. Simmons, Palindromic powers, J. Rec. Math., 3 (No. 2, 1970), 9398. [Annotated scanned copy] See page 95.


FORMULA

Equals A263619(2n)1.


MATHEMATICA

Table[Length[Select[Range[1, Floor[Sqrt[10^(2 n)]]], PalindromeQ[#^2] &]], {n, 6}] (* Robert Price, Apr 26 2019 *)


PROG

(Python)
def ispal(n): s = str(n); return s == s[::1]
def a(n):
c, k, kk = 0, 1, 1
while kk < 10**(2*n): c, k, kk = c + (ispal(kk)), k+1, kk + 2*k + 1
return c
print([a(n) for n in range(1, 8)]) # Michael S. Branicky, Mar 06 2021


CROSSREFS

Cf. A002778, A002779, A263617, A263617, A263618, A263619.
Sequence in context: A075390 A118523 A097633 * A083356 A096337 A175318
Adjacent sequences: A263617 A263618 A263619 * A263621 A263622 A263623


KEYWORD

nonn,base,more


AUTHOR

N. J. A. Sloane, Oct 23 2015


EXTENSIONS

a(7)a(10) from Chai Wah Wu, Oct 25 2015


STATUS

approved



