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Integers expressible as the sum of a square and a triangular number in just one way.
4

%I #10 Dec 08 2019 12:24:35

%S 1,2,3,4,5,6,11,12,14,16,17,21,24,25,29,30,32,35,36,39,42,44,49,50,51,

%T 53,54,56,57,65,66,71,72,74,75,77,78,80,81,84,95,96,101,104,105,107,

%U 110,116,117,119,120,122,126,128,129,131,137,141,149,150,152,153,156,161

%N Integers expressible as the sum of a square and a triangular number in just one way.

%C It is assumed here that 0 is a square but not a triangular number. - _Amiram Eldar_, Dec 08 2019

%H Amiram Eldar, <a href="/A082657/b082657.txt">Table of n, a(n) for n = 1..10000</a>

%t aQ[n_] := Length @ Solve[x^2 + y (y + 1)/2 == n && x >= 0 && y > 0, {x, y}, Integers] == 1; Select[Range[161], aQ] (* _Amiram Eldar_, Dec 08 2019 *)

%Y Cf. A000217, A000290, A082658, A082659, A082660.

%K nonn

%O 1,2

%A _Jason Earls_, May 17 2003