%I A064322
%S A064322 0,1,21,231,1540,7260,26796,82621,222111,536130,1186570,2445366,
%T A064322 4747821,8763391,15487395,26357430,43398586,69401871,108140571,
%U A064322 164629585,245433090,359026206,516216646,730632651,1019283825
%N A064322 Triply triangular numbers.
%H A064322 Harry J. Smith, <a href="b064322.txt">Table of n, a(n) for n=0,...,400</
               a>
%F A064322 a(n) = A000217(A000217(A000217(n))) = n*(n+1)*(n^2+n+2)*(n^4+2n^3+n^2+2n^2+2n+8)/
               128 = A002817(n)*(A002817(n)+1)/2
%e A064322 a(4)=1540 because 4th triangular number is 10, 10th triangular number 
               is 55 and 55th triangular number is 1540.
%t A064322 f[n_] := n(n + 1)/2; Table[ Nest[f, n, 3], {n, 0, 25}] (from Robert G. 
               Wilson v Jun 30 2004)
%o A064322 (PARI) Tri(n)= { n*(n + 1)/2 } { for (n=0, 400, write("b064322.txt", 
               n, " ", Tri(Tri(Tri(n)))) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), 
               Sep 11 2009]
%Y A064322 Cf. A000217, A002817, A066370.
%Y A064322 Sequence in context: A027812 A027508 A020267 this_sequence A126902 A010973 
               A022586
%Y A064322 Adjacent sequences: A064319 A064320 A064321 this_sequence A064323 A064324 
               A064325
%K A064322 nonn
%O A064322 0,3
%A A064322 Henry Bottomley (se16(AT)btinternet.com), Oct 15 2001