This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A256398 #40 Aug 22 2025 07:40:24
%S A256398 0,2,8,101,242,404,585,909,10001,12221,14841,20402,24642,40004,44244,
%T A256398 48884,50805,90009,96269,1000001,1030301,1080801,1210121,1244421,
%U A256398 1298921,1440441,1478741,1690961,2004002,2234322,2468642,2484842,4000004,4050504,4410144
%N A256398 Palindromes of the form i^2 + reverse(i)^2.
%C A256398 Is 864666666468 the only term in this sequence that has an even number of digits? - _Jon E. Schoenfield_, Mar 30 2015
%C A256398 The next terms with an even number of digits are 5807785995877085, 56359464311346495365, and 943614966934439669416349, which are obtained for i = 37939066, 3553782166, 529145826418 (and their reverses). - _Giovanni Resta_, Aug 22 2025
%H A256398 Bui Quang Tuan, <a href="/A256398/b256398.txt">Table of n, a(n) for n = 1..458</a>
%e A256398 Palindrome 585 is in the sequence because 585 = 12^2 + 21^2.
%e A256398 The smallest term that can be obtained in more than one way is 125484521 = 11020^2 + 2011^2 = 11200^2 + 211^2. Are there any terms that can be obtained in more than two ways? - _Jon E. Schoenfield_, Mar 30 2015
%t A256398 Sort@ DeleteDuplicates@ Select[Table[n^2 + FromDigits[Reverse[IntegerDigits@ n]]^2, {n, 10000}], Reverse@ IntegerDigits@ # == IntegerDigits@ # &] (* _Michael De Vlieger_, Mar 28 2015 *)
%o A256398 (PARI) rev(n)=r="";d=digits(n);for(i=1,#d,r=concat(Str(d[i]),r));eval(r)
%o A256398 v=[];for(n=0,10^4,if(rev(P=(n^2+rev(n)^2))==P,v=concat(v,P)));vecsort(v,,8) \\ _Derek Orr_, Mar 29 2015
%Y A256398 Cf. A002113 (palindromes), A056964 (n+rev(n)).
%Y A256398 Cf. A256437.
%K A256398 nonn,base,changed
%O A256398 1,2
%A A256398 _Bui Quang Tuan_, Mar 28 2015
%E A256398 Data corrected by _Derek Orr_, Mar 29 2015