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A098690
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Number of solutions to rev(x^2)=rev(x)^2 below 10^n.
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0
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3, 9, 24, 63, 153, 362, 819, 1810, 3872, 8160, 16681, 33756, 66864, 130937, 251982, 480793, 903981, 1685563, 3106008, 5677863, 10276935, 18464658, 32891187, 58169964, 102136772, 178096364, 308593319, 531191384, 909227946, 1546356485, 2617639292
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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For n = 2 the a(2) = 9 solutions are 1, 2, 3, 11, 12, 13, 21, 22, 31. - David Radcliffe, Aug 28 2021
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MATHEMATICA
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f[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Differences[Table[Length[Select[Range[10^n], f[#^2]==f[#]^2&]], {n, 0, 6}]] (* Geoffrey Critzer, Dec 18 2013 *)
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PROG
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(Python)
def rev(n): return int(str(n)[::-1])
def a(n): return sum(k % 10 and rev(k**2) == rev(k)**2 for k in range(10**n)) # David Radcliffe, Aug 28 2021
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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