cp's OEIS Frontend

A033294 Squares which when written backwards remain square (final 0's excluded).

%I A033294 #34 Jun 07 2023 04:44:13
%S A033294 1,4,9,121,144,169,441,484,676,961,1089,9801,10201,10404,10609,12321,
%T A033294 12544,12769,14641,14884,40401,40804,44521,44944,48841,69696,90601,
%U A033294 94249,96721,698896,1002001,1004004,1006009,1022121,1024144,1026169
%N A033294 Squares which when written backwards remain square (final 0's excluded).
%C A033294 Of this sequence's first 10000 terms, only nine have an even number of digits; see A354256.
%H A033294 Jon E. Schoenfield, <a href="/A033294/b033294.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Reinhard Zumkeller)
%H A033294 <a href="/index/Sq#sqrev">Index entry for sequences related to reversing digits of squares</a>
%e A033294 144 = 12 * 12 is a term because 441 = 21 * 21.
%t A033294 Select[Range[1100]^2,Mod[#,10]!=0&&IntegerQ[Sqrt[FromDigits[Reverse[ IntegerDigits[ #]]]]]&] (* _Harvey P. Dale_, Oct 28 2013 *)
%o A033294 (Haskell)
%o A033294 a033294 n = a033294_list !! (n-1)
%o A033294 a033294_list = filter chi a000290_list where
%o A033294   chi m = m `mod` 10 > 0 && head ds `elem` [1,4,5,6,9] &&
%o A033294           a010052 (foldl (\v d -> 10 * v + d) 0 ds) == 1 where
%o A033294     ds = unfoldr
%o A033294          (\x -> if x == 0 then Nothing else Just $ swap $ divMod x 10) m
%o A033294 -- _Reinhard Zumkeller_, Jan 19 2012
%o A033294 (Python)
%o A033294 from math import isqrt
%o A033294 from itertools import count, islice
%o A033294 def sqr(n): return isqrt(n)**2 == n
%o A033294 def agen():
%o A033294     yield from (k*k for k in count(1) if k%10 and sqr(int(str(k*k)[::-1])))
%o A033294 print(list(islice(agen(), 36))) # _Michael S. Branicky_, May 21 2022
%Y A033294 Subsequence of A115690.
%Y A033294 Cf. A007488, A007500, A061457, A354256.
%K A033294 base,nonn
%O A033294 1,2
%A A033294 _Jeff Burch_
%E A033294 More terms from _Erich Friedman_
%E A033294 Initial 0 removed and offset changed by _Reinhard Zumkeller_, Jan 19 2012