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A124664 Both k and its reverse are one more than a square.

%I A124664 #21 Aug 13 2020 14:02:28
%S A124664 1,2,5,10,50,101,626,730,1090,2210,5477,7745,10001,10610,71290,227530,
%T A124664 1000001,1010026,1014050,1040401,2217122,2676497,5053505,5631130,
%U A124664 6200101,6265010,7946762,100000001,101808101,248157010,10000000001,10180608202,10182828101
%N A124664 Both k and its reverse are one more than a square.
%C A124664 The first digit for each term is either 1, 2, 5, 6 or 7. - _Chai Wah Wu_, May 25 2017
%H A124664 Chai Wah Wu, <a href="/A124664/b124664.txt">Table of n, a(n) for n = 1..100</a>
%H A124664 Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a>. See 5477 and 7745.
%e A124664 5477 is in the sequence because 5477 = 74^2 + 1 and 7745 = 88^2 + 1.
%p A124664 r:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||n):
%p A124664 select(x-> issqr(r(x)-1), [n^2+1$n=0..150000])[]; # _Alois P. Heinz_, May 24 2017
%t A124664 Select[Range[10000000], IntegerQ[Sqrt[ # - 1]] && IntegerQ[Sqrt[FromDigits[Reverse[IntegerDigits[ # ]]] - 1]] &]
%Y A124664 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.
%Y A124664 Cf. A287389: both k and its reverse are one less than a square.
%K A124664 nonn,base
%O A124664 1,2
%A A124664 _Tanya Khovanova_, Dec 23 2006
%E A124664 More terms from _Alois P. Heinz_, May 24 2017