A185980 Nontriangular numbers that are the sum of two (positive) triangular numbers in more than one way.

16, 31, 42, 46, 51, 56, 72, 76, 81, 94, 106, 111, 121, 123, 126, 133, 141, 146, 156, 157, 172, 174, 181, 186, 191, 196, 198, 211, 216, 225, 226, 237, 241, 246, 256, 259, 268, 281, 286, 289, 291, 297, 301, 306, 310, 315, 321, 326, 328, 331, 336, 342, 346, 354

Offset

1,1

Comments

A000217(0)=0, but it will not appear as a summand.

A185979 uses only positive triangular summands, and includes triagonal (or body diagonal) numbers like 231, 276, 406, 666, ...

Links

Table of n, a(n) for n=1..54.

Formula

See the one given for A185978, taking into account multiplicities.

Example

16 = 15 + 1 = 10 + 6.
81 = 45 + 36 = 66 + 15 = 78 + 3.

Crossrefs

Cf. A000217, A020756 (sums of two triangular numbers), A051533 (sums of two positive triangular numbers), A064816, A185978, A185979.

Sequence in context: A257349 A167997 A185979 * A064816 A262749 A265134

Adjacent sequences: A185977 A185978 A185979 * A185981 A185982 A185983

Keyword

nonn,easy

Author

Wolfdieter Lang, Feb 15 2011

Status

approved