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 A263616 Number of n-digit numbers whose square is a palindrome. 1
 4, 3, 8, 5, 11, 6, 19, 14, 25, 18, 49, 31, 71, 46, 105, 71, 154, 101, 209, 132, 292, 182 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Number of terms in A002778 with exactly n digits. LINKS Table of n, a(n) for n=1..22. G. J. Simmons, Palindromic powers, J. Rec. Math., 3 (No. 2, 1970), 93-98. [Annotated scanned copy] See page 95. EXAMPLE a(2) = 3 because there are three 2-digit numbers with palindromic squares: 11^2 = 121, 22^2 = 484, 26^2 = 676. MATHEMATICA Join[{4}, Table[Total[Table[If[PalindromeQ[n^2], 1, 0], {n, 10^x, 10^(x+1)-1}]], {x, 9}]] (* Harvey P. Dale, Apr 09 2019 *) PROG (Python) from itertools import product def pal(n): s = str(n); return s == s[::-1] def a(n): return int(n==1) + sum(pal(i**2) for i in range(10**(n-1), 10**n)) print([a(n) for n in range(1, 8)]) # Michael S. Branicky, Apr 03 2021 CROSSREFS Cf. A002778, A002779, A263617, A263618. Sequence in context: A227242 A156028 A021232 * A280166 A257088 A022998 Adjacent sequences: A263613 A263614 A263615 * A263617 A263618 A263619 KEYWORD nonn,base,more AUTHOR N. J. A. Sloane, Oct 23 2015 EXTENSIONS a(9)-a(10) from Chai Wah Wu, Oct 25 2015 a(11) from Michael S. Branicky, Apr 03 2021 a(12)-a(22) (using A002778) from Chai Wah Wu, Sep 16 2021 STATUS approved

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Last modified February 27 21:03 EST 2024. Contains 370378 sequences. (Running on oeis4.)