A136650 Self-convolution of A006125(n) = 2^{n(n-1)/2}.

1, 2, 5, 20, 148, 2208, 67904, 4264960, 541216768, 137984868352, 70507295670272, 72128242290524160, 147646152060442771456, 604610628447525580832768, 4952364915780360673188380672, 81134591384874923825347187179520

Offset: 0

Author

Paul D. Hanna, Jan 16 2008

Keywords

• nonn

Programs

PARI

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

Formula

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