cp's OEIS Frontend

A038206 Can express a(n) with the digits of a(n)^2 in order, only adding plus signs.

%I A038206 #29 Oct 06 2021 17:58:23
%S A038206 0,1,9,10,36,45,55,82,91,99,100,235,297,369,370,379,414,657,675,703,
%T A038206 756,792,909,918,945,964,990,991,999,1000,1296,1702,1782,2223,2728,
%U A038206 3366,3646,3682,4132,4879,4906,4950,5050,5149,5292,6832,7191,7272,7389
%N A038206 Can express a(n) with the digits of a(n)^2 in order, only adding plus signs.
%C A038206 Every term is congruent to 0 or 1 modulo 9.
%H A038206 Max Alekseyev and Giovanni Resta, <a href="/A038206/b038206.txt">Table of n, a(n) for n = 1..3200</a> (first 408 terms from Max Alekseyev)
%F A038206 a(n) = sqrt(A104113(n)). - _Andrea Tarantini_, Sep 27 2021
%e A038206 82^2 = 6724 and 6+72+4 = 82.
%o A038206 (Python)
%o A038206 def expr(t, d): # can you express target t with digits d, only adding +'s
%o A038206     if t < 0: return False
%o A038206     if t == int(d): return True
%o A038206     return any(expr(t-int(d[:i]), d[i:]) for i in range(1, len(d)))
%o A038206 def ok(n): return expr(n, str(n*n))
%o A038206 print(list(filter(ok, range(7500)))) # _Michael S. Branicky_, Sep 27 2021
%Y A038206 Cf. A104113 (squared).
%K A038206 nonn,base
%O A038206 1,3
%A A038206 _Erich Friedman_
%E A038206 Offset corrected and b-file added by _Max Alekseyev_, Jun 08 2018