This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A236415 Sequence of distinct least triangular numbers such that the arithmetic mean of the first n terms is also a triangular number. Initial term is 0. 0
 0, 6, 3, 15, 741, 153, 25878, 3828, 16653, 253, 4753, 23653, 6328, 53956, 9730, 191890, 21115, 140185, 1225, 26335, 317206, 3160, 38503, 2108431, 37950, 121278, 1440905403, 53483653, 201733741, 58595725, 22663524351, 787786971, 23483020686, 1475521326 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence is believed to be infinite. If a(31) exists, it will be greater than 10^10. a(31)=22663524351. - Jon E. Schoenfield, Feb 07 2014 LINKS EXAMPLE a(1) = 0. a(2) must be a triangular number such that (a(1)+a(2))/2 is triangular. Thus, a(1) = 6. a(3) must be a triangular number such that (a(1)+a(2)+a(3))/3 is triangular. Thus, a(3) = 3. ...and so on PROG (Python) def Tri(x): ..for n in range(10**10): ....if x == n*(n+1)/2: ......return True ....if x < n*(n+1)/2: ......return False ..return False def TriAve(init): ..print(init) ..lst = [] ..lst.append(init) ..n = 1 ..while n*(n+1)/2 < 10**10: ....if n*(n+1)/2 not in lst: ......if Tri(((sum(lst)+int(n*(n+1)/2))/(len(lst)+1))): ........print(int(n*(n+1)/2)) ........lst.append(int(n*(n+1)/2)) ........n = 1 ......else: ........n += 1 ....else: ......n += 1 CROSSREFS Cf. A000217. Sequence in context: A302350 A046879 A248267 * A267831 A231881 A229005 Adjacent sequences:  A236412 A236413 A236414 * A236416 A236417 A236418 KEYWORD nonn AUTHOR Derek Orr, Jan 25 2014 EXTENSIONS More terms from Jon E. Schoenfield, Feb 07 2014 STATUS approved

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

Last modified August 24 13:48 EDT 2019. Contains 326279 sequences. (Running on oeis4.)