login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A350367 Triangular numbers that are the sum of two distinct nonzero triangular numbers in more than one way. 0
231, 276, 406, 666, 861, 1081, 1225, 1431, 1711, 1891, 2211, 2556, 3081, 3741, 3916, 4186, 4371, 4560, 4656, 5151, 5356, 5671, 5886, 6786, 7021, 7381, 7875, 8001, 8128, 8256, 8778, 9316, 10731, 11781, 12246, 12561, 12720, 13366, 13861, 14196, 14706, 15576 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
231 = 21 + 210 = 78 + 153.
276 = 45 + 231 = 66 + 210 = 105 + 171.
MATHEMATICA
(P=PolygonalNumber)[3, Select[Range@176, Length@Select[Subsets[P[3, Range[s=#]], {2}], Total@#==P[3, s]&]>1&]] (* Giorgos Kalogeropoulos, Dec 31 2021 *)
PROG
(Python)
from collections import Counter
from itertools import count, takewhile, combinations as combs
def aupto(limit):
tris = takewhile(lambda x: x <= limit, (k*(k+1)//2 for k in count(1)))
trilst = list(tris); triset = set(trilst)
tri2ct = Counter(sum(c) for c in combs(trilst, 2) if sum(c) in triset)
return sorted(t for t in tri2ct if t <= limit and tri2ct[t] > 1)
print(aupto(16000)) # Michael S. Branicky, Dec 27 2021
CROSSREFS
Intersection of A000217 and A262749.
Sequence in context: A345795 A088289 A046009 * A337231 A117223 A160355
KEYWORD
nonn
AUTHOR
Shyam Sunder Gupta, Dec 27 2021
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 28 07:05 EST 2024. Contains 370387 sequences. (Running on oeis4.)