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 A307717 Number of palindromic squares, k^2, of length n such that k is also palindromic. 3
 4, 0, 2, 0, 5, 0, 3, 0, 8, 0, 5, 0, 13, 0, 9, 0, 22, 0, 16, 0, 37, 0, 27, 0, 60, 0, 43, 0, 93, 0, 65, 0, 138, 0, 94, 0, 197, 0, 131, 0, 272, 0, 177, 0, 365, 0, 233, 0, 478, 0, 300, 0, 613, 0, 379, 0, 772, 0, 471, 0, 957, 0, 577, 0, 1170, 0, 698, 0, 1413, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Is a(2n) always zero? LINKS P. De Geest, Palindromic Squares Eric Weisstein's World of Mathematics, Palindromic Number EXAMPLE There are only two palindromic squares of length 3 whose root is also palindromic. 11^2=121 and 22^2=484.  Thus, a(3)=2. MATHEMATICA Table[Length[Select[Range[If[n == 1, 0, Ceiling[Sqrt[10^(n - 1)]]], Floor[Sqrt[10^n]]], # == IntegerReverse[#] && #^2 == IntegerReverse[#^2] &]], {n, 15}] CROSSREFS Cf. A002778, A002779, A034307, A034822. Sequence in context: A319037 A067565 A243154 * A226782 A010635 A272198 Adjacent sequences:  A307714 A307715 A307716 * A307718 A307719 A307720 KEYWORD nonn,base,hard AUTHOR Robert Price, Apr 23 2019 EXTENSIONS a(16)-a(20) from Robert Price, Apr 25 2019 a(21)-a(70) from Giovanni Resta, Apr 28 2019 STATUS approved

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Last modified September 27 11:41 EDT 2020. Contains 337380 sequences. (Running on oeis4.)