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

Author

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

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Subsequence of A264961 and of A085780.

Programs

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

Extensions

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