A064816 Numbers which are the sums of two positive triangular numbers (A000217) in exactly two different ways.

16, 31, 42, 46, 51, 56, 72, 76, 94, 111, 121, 123, 126, 133, 141, 146, 157, 172, 174, 186, 191, 196, 198, 216, 225, 226, 231, 237, 241, 246, 259, 268, 281, 286, 289, 291, 297, 301, 306, 310, 315, 321, 326, 328, 336, 342, 346, 354, 366, 367, 379, 380, 384

Offset: 1

Author

Jonathan Ayres (jonathan.ayres(AT)btinternet.com), Oct 22 2001

Keywords

• nonn

Comments

Note that A000217(0)=0, so even 6 = 6 + 0 = 3 + 3, it is not a member of this sequence. - Wolfdieter Lang, Feb 15 2011

Examples

			16 = 15 + 1 = 10 + 6.
		

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Programs

PARI

Tri(n)= { n*(n + 1)/2 } { n=0; for (m=1, 10^9, k=0; i=1; until (t>=m\2 || k>2, t=Tri(i); j=i; i++; until (s>=m || k>2, s=t + Tri(j); j++; if (s==m, k++))); if (k==2, write("b064816.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Sep 27 2009

Extensions

Offset changed from 0 to 1 by Harry J. Smith, Sep 27 2009

Name corrected by Wolfdieter Lang, Feb 15 2011