0,2

When aerated, gives Hankel transform of A138175. sqrt(abs(a(n))/2^n=A005156(n).

A. V. Razumov and Yu. G. Stroganov, On refined enumerations of some symmetry classes of alternating sign matrices

a(n)=(-1)^n*product{k=1..n, (6k-2)!(2k-1)!/((4k-1)!(4k-2)!)}^2

Sequence in context: A084703 A122747 A069135 this_sequence A055209 A030450 A041629

Adjacent sequences: A138173 A138174 A138175 this_sequence A138177 A138178 A138179

easy,sign

Paul Barry (pbarry(AT)wit.ie), Mar 03 2008