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A124664
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Both k and its reverse are one more than a square.
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2
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1, 2, 5, 10, 50, 101, 626, 730, 1090, 2210, 5477, 7745, 10001, 10610, 71290, 227530, 1000001, 1010026, 1014050, 1040401, 2217122, 2676497, 5053505, 5631130, 6200101, 6265010, 7946762, 100000001, 101808101, 248157010, 10000000001, 10180608202, 10182828101
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OFFSET
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1,2
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COMMENTS
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The first digit for each term is either 1, 2, 5, 6 or 7. - Chai Wah Wu, May 25 2017
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LINKS
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EXAMPLE
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5477 is in the sequence because 5477 = 74^2 + 1 and 7745 = 88^2 + 1.
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MAPLE
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r:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||n):
select(x-> issqr(r(x)-1), [n^2+1$n=0..150000])[]; # Alois P. Heinz, May 24 2017
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MATHEMATICA
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Select[Range[10000000], IntegerQ[Sqrt[ # - 1]] && IntegerQ[Sqrt[FromDigits[Reverse[IntegerDigits[ # ]]] - 1]] &]
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CROSSREFS
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A066618 is a subsequence of this sequence of numbers that do not end in 0. The sequence A027720 = Palindromes of form n^2 + 1 - is a palindromic subsequence of this sequence.
Cf. A287389: both k and its reverse are one less than a square.
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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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