A140422 Half the number of n X n symmetric binary matrices with every 1 adjacent to some 0 horizontally or vertically and every 0 adjacent to some 1 horizontally or vertically.
1, 5, 47, 849, 29241, 1901849, 234932757, 55047807551, 24470603864937, 20637055514911557, 33018065501295740951, 100220335496292824426843, 577112450349963078523926227
Offset: 2