%I A143689
%S A143689 1,2,6,13,23,36,52,71,93,118,146,177,211,248,288,331,377,426,478,533,
%T A143689 591,652,716,783,853,926,1002,1081,1163,1248,1336,1427,1521,1618,1718,
%U A143689 1821,1927,2036,2148,2263,2381,2502,2626,2753,2883,3016,3152,3291
%N A143689 a(n) = A000326(n+1) - 3n.
%C A143689 Equals left border of triangle A033292
%F A143689 a(n) = A000326(n+1) - 3n. A000326 = pentagonal numbers. Equals binomial 
               transform of [1, 1, 3, 0, 0, 0,...].
%F A143689 a(n) = (3n^2-n+2)/2 = A027599(n+1)/2. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Sep 03 2008
%F A143689 a(n)=3*n+a(n-1)-5 (with a(1)=1) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), 
               Nov 09 2009]
%e A143689 a(4) = 23 = A000326(5) - 12 = (35 - 12).
%e A143689 a(4) = 23 = (1, 4, 6, 4, 1) dot (1, 1, 3, 0, 0) = (1 + 4 + 18 + 0 + 0).
%e A143689 For n=2, a(2)=3*2+1-5=2; n=3, a(3)=3*3+2-5=6; n=4, a(4)=3*4+6-5=13 [From 
               Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 09 2009]
%Y A143689 Cf. A000326, A033292.
%Y A143689 Sequence in context: A026052 A049616 A064960 this_sequence A011891 A003600 
               A000135
%Y A143689 Adjacent sequences: A143686 A143687 A143688 this_sequence A143690 A143691 
               A143692
%K A143689 nonn,new
%O A143689 0,2
%A A143689 Gary W. Adamson (qntmpkt(AT)yahoo.com), Aug 29 2008
%E A143689 Corrected index of A000326 in definition, formula and example. - R. J. 
               Mathar, Sep 03 2008
%E A143689 More terms a(15)-a(48)from Vincenzo Librandi (vincenzo.librandi(AT)tin.it), 
               Nov 09 2009