%I
%S 1233,8833,990100,94122353,1765038125,2584043776,7416043776,
%T 8235038125,9901009901,116788321168,123288328768,876712328768,
%U 883212321168,999900010000,13793103448276,15348303604525,84651703604525,86206903448276,91103202846976,92318202663025
%N Numbers, with an even number of digits, that are the sum of the squares of their two halves (leading zeros allowed only for the second half).
%C The sequence is infinite since it contains several infinite subsequences (see A055617, etc.).
%C If x = A*10^n+B is an element not beginning with 9, then (10^nA)*10^n+B is another (e.g. 1233 <> 8833).
%C Numbers that can be written as n = A*10^d + B with 10^(d1) <= A < 10^d, 0 <= B < 10^d, and A^2 + B^2 = n.  _Robert Israel_, May 10 2015
%H Robert Israel, <a href="/A055616/b055616.txt">Table of n, a(n) for n = 1..1000</a>
%e 8833 is ok, since 8833 = 88^2 + 33^2.
%p dmax:= 8: # to get all entries with at most 2*dmax digits
%p Res:= NULL:
%p for d from 2 to dmax do
%p cands:= map(t > subs(t,[x,y]), [isolve(x^2 + y^2 = 10^(2*d)+1)]);
%p cands:= select(t > t[1]::even and t[1]>=0 and t[2]>0, cands);
%p cands:= map(t > ([(10^d + t[1])/2, (t[2]+1)/2], [(10^dt[1])/2, (t[2]+1)/2]), cands);
%p cands:= select(t > (t[1]>= 10^(d1) and t[1] < 10^d and t[2] <= 10^d), cands);
%p Res:= Res, op(map(t > 10^d*t[1]+t[2], cands));
%p od:
%p sort([Res]); # _Robert Israel_, May 10 2015
%t fQ[n_] := Block[{d = IntegerDigits@ n}, If[OddQ[Length@ d], False, Plus[FromDigits[Take[d, Length[d]/2]]^2, FromDigits[Take[d, Length[d]/2]]^2]] == n]; Select[Range@ 1000000, fQ] (* _Michael De Vlieger_, May 09 2015 *)
%o (Python)
%o def a():
%o ..n = 1
%o ..while n < 10**6:
%o ....st = str(n)
%o ....if len(st) % 2 == 0:
%o ......s1 = st[:int(len(st)/2)]
%o ......s2 = st[int(len(st)/2):int(len(st))]
%o ......if int(s1)**2+int(s2)**2 == int(st):
%o ........print(n,end=', ')
%o ........n += 1
%o ......else:
%o ........n += 1
%o ....else:
%o ......n = 10*n
%o a()
%o # _Derek Orr_, Jul 08 2014
%Y Cf. A064942 for the number of solutions, where leading zeros are allowed.
%Y Cf. A055617, A055618, A055619.
%K nonn,base
%O 1,1
%A Ulrich Schimke (ulrschimke(AT)aol.com)
%E Definition corrected by _Derek Orr_, Jul 09 2014
