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A263620 Number of nonzero palindromic squares with at most 2n digits. 3
3, 6, 14, 19, 30, 36, 55, 69, 94, 112 (list; graph; refs; listen; history; text; internal format)
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), 93-98. [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

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Last modified November 29 08:47 EST 2022. Contains 358422 sequences. (Running on oeis4.)