A112355 - OEIS

A112355

Triangular numbers that are the sum of three positive triangular numbers.

3, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666, 703, 741, 780, 820, 861, 903, 946, 990, 1035, 1081, 1128, 1176, 1225, 1275, 1326

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OFFSET

1,1

COMMENTS

A112353 is a subsequence: it requires the three positive triangular numbers to be distinct. The positive terms of A076140 are a subsequence.

LINKS

Table of n, a(n) for n=1..49.

EXAMPLE

21 is a term because 21 = 3 + 3 + 15 and these four numbers are positive triangular numbers (A000217(6) = A000217(2) + A000217(2) + A000217(5)). {Also 21 = 1 + 10 + 10 = A000217(1) + A000217(4) + A000217(4).}.

CROSSREFS

Cf. A000217 (triangular numbers), A089982 (triangular numbers that are the sum of two positive triangular numbers), A112353, A076140 (the three triangular numbers summed are identical).

Sequence in context: A173600 A328987 A108770 * A074314 A077759 A278291

Adjacent sequences: A112352 A112353 A112354 * A112356 A112357 A112358

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Sep 06 2005

STATUS

approved