The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A064322 Triply triangular numbers. 5
 0, 1, 21, 231, 1540, 7260, 26796, 82621, 222111, 536130, 1186570, 2445366, 4747821, 8763391, 15487395, 26357430, 43398586, 69401871, 108140571, 164629585, 245433090, 359026206, 516216646, 730632651, 1019283825, 1403201800, 1908167976, 2565535896, 3413156131 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Harry J. Smith, Table of n, a(n) for n = 0..400 FORMULA a(n) = A000217(A000217(A000217(n))) = n*(n+1)*(n^2 + n + 2)*(n^4 + 2n^3 + 3n^2 + 2n + 8)/128 = A002817(n)*(A002817(n) + 1)/2. G.f.: x*(1 + 12*x + 78*x^2 + 133*x^3 + 78*x^4 + 12*x^5 + x^6)/(1-x)^9. [Colin Barker, Apr 19 2012] EXAMPLE a(4) = 1540 because 4th triangular number is 10, 10th triangular number is 55 and 55th triangular number is 1540. MAPLE a:= n-> ((k-> binomial(k+1, 2))@@3)(n): seq(a(n), n=0..30);  # Alois P. Heinz, Apr 19 2012 MATHEMATICA f[n_] := n(n + 1)/2; Table[ Nest[f, n, 3], {n, 0, 25}] (* Robert G. Wilson v, Jun 30 2004 *) PROG (PARI) Tri(n)= { n*(n + 1)/2 } { for (n=0, 400, write("b064322.txt", n, " ", Tri(Tri(Tri(n)))) ) } \\ Harry J. Smith, Sep 11 2009 CROSSREFS Cf. A000217, A002817, A066370. Sequence in context: A320588 A020267 A188354 * A126902 A162646 A247615 Adjacent sequences:  A064319 A064320 A064321 * A064323 A064324 A064325 KEYWORD nonn,easy AUTHOR Henry Bottomley, Oct 15 2001 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 April 10 14:07 EDT 2021. Contains 342845 sequences. (Running on oeis4.)