%I A129863
%S A129863 6,18,39,69,108,156,213,279,354,438,531,633,744,864,993,1131,1278,1434,
%T A129863 1599,1773,1956,2148,2349,2559,2778,3006,3243,3489,3744,4008,4281,4563,
%U A129863 4854,5154,5463,5781,6108,6444,6789,7143,7506,7878,8259,8649,9048,9456
%N A129863 Sums of three consecutive pentagonal numbers.
%C A129863 Arises in pentagonal number analogue to A129803 Triangular numbers which 
               are the sum of three consecutive triangular numbers. What are the 
               pentagonal numbers which are the sum of three consecutive pentagonal 
               numbers?
%F A129863 a(n) = P(n) + P(n+1) + P(n+2) where P(n) = A000326(n) = n(3n-1)/2.
%F A129863 a(n) = P(n) + P(n+1) + P(n+2) where P(n) = A000326(n) = n(3n-1)/2. For 
               n = 0, 1, 2, ... a(n+1) = (9/2)*(n^2) + (15/2)*n + 6.
%F A129863 a(n) = (3n^2+5n+4)*(3/2) - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), 
               May 27 2007
%e A129863 a(1) = 6 = A000326(0) + A000326(1) + A000326(2) = 0 + 1 + 5.
%e A129863 a(2) = 18 = A000326(1) + A000326(2) + A000326(3) = 1 + 5 + 12.
%t A129863 Table[(3/2)*(4 + 5*n + 3*n^2), {n, 0, 100}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), 
               May 27 2007
%Y A129863 Cf. A000326, A007667, A034961, A129803.
%Y A129863 Sequence in context: A101853 A132432 A005899 this_sequence A035489 A122061 
               A002411
%Y A129863 Adjacent sequences: A129860 A129861 A129862 this_sequence A129864 A129865 
               A129866
%K A129863 easy,nonn
%O A129863 1,1
%A A129863 Jonathan Vos Post (jvospost3(AT)gmail.com), May 23 2007, May 24 2007