A136650 - OEIS

%I #2 Mar 30 2012 18:37:09

%S 1,2,5,20,148,2208,67904,4264960,541216768,137984868352,

%T 70507295670272,72128242290524160,147646152060442771456,

%U 604610628447525580832768,4952364915780360673188380672,81134591384874923825347187179520

%N Self-convolution of A006125(n) = 2^{n(n-1)/2}.

%F a(n) = Sum_{k=0..n} 2^{ k(k-1)/2 + (n-k)(n-k-1)/2 }.

%o (PARI) a(n)=sum(k=0,n,2^(k*(k-1)/2 + (n-k)*(n-k-1)/2))

%K nonn

%O 0,2

%A _Paul D. Hanna_, Jan 16 2008