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A035519
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Rare numbers: k-r and k+r are both perfect squares, where r is reverse of k and k is non-palindromic.
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5
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65, 621770, 281089082, 2022652202, 2042832002, 868591084757, 872546974178, 872568754178, 6979302951885, 20313693904202, 20313839704202, 20331657922202, 20331875722202, 20333875702202, 40313893704200
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OFFSET
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1,1
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COMMENTS
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All non-palindromic numbers m = a^2 + b^2 such that reversal(m) = 2*a*b are terms of this sequence. For the numbers with this property, m - reversal(m) = (a-b)^2 and m + reversal(m) = (a+b)^2. - Metin Sariyar, Dec 19 2019
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REFERENCES
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Shyam Sunder Gupta, Systematic computations of rare numbers, The Mathematics Education, Vol. XXXII, No. 3, Sept. 1998.
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LINKS
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EXAMPLE
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65 - 56 = 9 and 65 + 56 = 121 are both squares.
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MATHEMATICA
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r[n_]:=FromDigits[Reverse[IntegerDigits[n, 10]], 10]; f[n_]:=n!=r[n]&&IntegerQ[Sqrt[n-r[n]]]&&IntegerQ[Sqrt[n+r[n]]]; Timing[lst={}; Do[If[f[n], AppendTo[lst, n]], {n, 11, 15!}]; lst] (* Vladimir Joseph Stephan Orlovsky, Oct 10 2009 *)
Select[Range[2043*10^6], !PalindromeQ[#]&&AllTrue[{Sqrt[#+ IntegerReverse[ #]], Sqrt[ #-IntegerReverse[#]]}, IntegerQ]&] (* The program generates the first 5 terms of the sequence. *) (* Harvey P. Dale, Jan 22 2023 *)
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PROG
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(PARI) isok(k) = {my(d = digits(k), rd = Vecrev(d), r = fromdigits(rd)); (d != Vecrev(d)) && issquare(k-r) && issquare(k+r); } \\ Michel Marcus, Jan 06 2020
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CROSSREFS
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KEYWORD
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nonn,base,nice
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AUTHOR
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STATUS
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approved
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