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

1,1

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

Links

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

Example

16 = 15 + 1 = 10 + 6.

Prog

(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

Crossrefs

Sequence in context: A167997 A185979 A185980 * A262749 A265134 A220000

Adjacent sequences: A064813 A064814 A064815 * A064817 A064818 A064819

Keyword

nonn

Author

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

Extensions

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

Name corrected by Wolfdieter Lang, Feb 15 2011

Status

approved