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%I #14 Apr 11 2014 02:35:32
%S 49,16856,40370463,678263443312,79792944561055313,
%T 65712442156478841194856,378818757978106938161558820799,
%U 15286701010761334171872123930835647200
%N Sum 7^((k^2+3k)/2) from k=1 to n.
%C Series of the kind m^((k^2+3k)/2) from k=1 to n was studied by Bernoulli and Euler.
%H Vincenzo Librandi, <a href="/A178190/b178190.txt">Table of n, a(n) for n = 1..40</a>
%p A178190:=n->add(7^((k^2 + 3*k)/2), k=1..n); seq(A178190(n), n=1..10); # _Wesley Ivan Hurt_, Apr 01 2014
%t aa = {}; m = 7; sum = 0; Do[sum = sum + m^((n + 3) n/2); AppendTo[aa, sum], {n, 1, 20}]; aa (* Artur Jasinski *)
%t Table[Sum[7^((k^2 + 3 k)/2), {k, n}], {n, 10}] (* _Wesley Ivan Hurt_, Apr 01 2014 *)
%o (PARI) a(n) = sum(k=1, n, 7^((k^2+3*k)/2)); \\ _Michel Marcus_, Sep 09 2013
%Y Cf. A178184-A178193.
%K nonn
%O 1,1
%A _Artur Jasinski_, May 21 2010
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