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A068084
Smallest triangular number which is a multiple (>1) of the n-th triangular number.
5
3, 6, 36, 120, 45, 105, 1176, 2016, 630, 990, 528, 780, 3003, 210, 3240, 32640, 9180, 11628, 2850, 630, 3003, 26565, 16836, 20100, 44850, 52650, 17766, 20706, 10440, 12090, 461280, 61776, 11781, 3570, 25200, 43956, 221445, 30381, 5460, 189420
OFFSET
1,1
LINKS
Zak Seidov and Chai Wah Wu, Table of n, a(n) for n = 1..10000 n = 1..1000 from Zak Seidov
EXAMPLE
The fifth triangular number is 15; the next triangular number that's divisible by 15 is 45, so a(5)=45.
MATHEMATICA
a[n_] := For[k=n+1, True, k++, If[Mod[k(k+1), n(n+1)]==0, Return[k(k+1)/2]]]
PROG
(Python)
from __future__ import division
def A068084(n):
u, v, t = 4*(n+1), (2*(n+1))**2-1, 4*n*(n+1)
while True:
if not v % t:
return v//8
v += u+1
u += 2 # Chai Wah Wu, Jan 13 2016
CROSSREFS
Sequence in context: A350991 A084260 A076983 * A003674 A211895 A240986
KEYWORD
easy,nonn
AUTHOR
Amarnath Murthy, Feb 18 2002
EXTENSIONS
Edited by Dean Hickerson, Feb 20 2002
STATUS
approved