|
Search: id:A066370
|
|
|
| A066370 |
|
Quadruply triangular numbers. |
|
+0
4
|
|
| 0, 1, 231, 26796, 1186570, 26357430, 359026206, 3413156131, 24666759216, 143717956515, 703974775735, 2989908659661, 11270904497931, 38398515291136, 119929709686710, 347357071281165, 941718655098991, 2408309883851256
(list; graph; listen)
|
|
|
OFFSET
|
0,3
|
|
|
COMMENT
|
See sequences A000217, A002817 and A064322 for triangular, doubly triangular and triply triangular numbers, respectively.
|
|
FORMULA
|
a(n) = n*(n + 1)*(n^2 + n + 2)*(n^4 + 2*n^3 + 3*n^2 + 2*n + 8)*(n^8 + 4*n^7 + 10*n^6 + 16*n^5 + 25*n^4 + 28*n^3 + 28*n^2 + 16*n + 128)/32768.
a(n) = A064322(n)*(A064322(n) + 1)/2 = A000217(A000217(A000217(A000217(n))))
|
|
EXAMPLE
|
a(2)=231 as A000217(A000217(A000217(A000217(2))))=231 is the second quadruply-triangular number.
|
|
MATHEMATICA
|
f[n_] := n(n + 1)/2; Table[ Nest[f, n, 4], {n, 0, 17}] (from Robert G. Wilson v Jun 30 2004)
|
|
CROSSREFS
|
Sequence in context: A029569 A152102 A152500 this_sequence A139412 A027551 A068750
Adjacent sequences: A066367 A066368 A066369 this_sequence A066371 A066372 A066373
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Brian Bayerle (bbayer03(AT)providence.edu), Dec 22 2001
|
|
|
Search completed in 0.002 seconds
|
