A110904 Integers that can be expressed as a product of triangular numbers in 3 different ways.

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

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: A333503 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