Number of even permutations on {1,2,...,n} with exactly 2 weak excedances.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =7a(5) =11a(6) =31a(7) =57a(8) =127a(9) =247a(10) =511a(11) =1013a(12) =2047a(13) =4083a(14) =8191a(15) =16369a(16) =32767a(17) =65519a(18) =131071a(19) =262125a(20) =524287a(21) =1048555a(22) =2097151a(23) =4194281a(24) =8388607a(25) =16777191a(26) =33554431a(27) =67108837a(28) =134217727a(29) =268435427