A026091 a(n) = T(4n,n), where T is the array defined in A026082.
1, 1, 18, 183, 1927, 20655, 224498, 2465815, 27304863, 304313548, 3409370698, 38362211823, 433219457730, 4907408334066, 55737813431070, 634528087334283, 7238225267825429, 82716464152842756, 946771870186411896, 10852263461880981957
Offset: 0