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A064816 Numbers which are the sums of two positive triangular numbers (A000217) in exactly two different ways. 9
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified March 24 19:33 EDT 2019. Contains 321448 sequences. (Running on oeis4.)