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A110904 Integers that can be expressed as a product of triangular numbers in 3 different ways. 2
630, 3780, 14850, 16380, 21420, 114660, 131670, 159390, 178200, 234360, 401940, 478800, 523260, 556920, 582120, 712530, 749700, 835380, 1455300, 1753290, 1936935, 2086920, 2162160, 2633400, 2841300, 3828825, 4791150, 5821200, 6056820, 6380010, 6396390, 6486480 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..1007

EXAMPLE

835380 = 91*9180 = 153*5460 = 630*1326.

PROG

(Python)

from __future__ import division

mmax = 10**3

tmax, A110904_dict = mmax*(mmax+1)//2, {}

ti = 0

for i in range(1, mmax+1):

    ti += i

    p = ti*i*(i-1)//2

    for j in range(i, mmax+1):

        p += ti*j

        if p <= tmax:

            A110904_dict[p] = A110904_dict[p]+1 if p in A110904_dict else 1

        else:

            break

A110904_list = sorted([i for i in A110904_dict if A110904_dict[i] == 3]) # Chai Wah Wu, Nov 29 2015

CROSSREFS

Subsequence of A264961 and of A085780.

Sequence in context: A177421 A173423 A295769 * A171258 A234245 A234241

Adjacent sequences:  A110901 A110902 A110903 * A110905 A110906 A110907

KEYWORD

nonn

AUTHOR

Luke T Pebody (ltp1000(AT)cam.ac.uk), Sep 21 2005

EXTENSIONS

a(19)-a(20) from R. J. Mathar, Nov 29 2015

STATUS

approved

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Last modified August 16 21:46 EDT 2018. Contains 313809 sequences. (Running on oeis4.)