Number of permutations of length n having exactly one descent such that the first element of the permutation is an odd number.

A257198

Number of permutations of length n having exactly one descent such that the first element of the permutation is an odd number.

Terms

    a(0) =0a(1) =0a(2) =2a(3) =6a(4) =16a(5) =36a(6) =78a(7) =162a(8) =332a(9) =672a(10) =1354a(11) =2718a(12) =5448a(13) =10908a(14) =21830a(15) =43674a(16) =87364a(17) =174744a(18) =349506a(19) =699030a(20) =1398080a(21) =2796180a(22) =5592382a(23) =11184786a(24) =22369596a(25) =44739216a(26) =89478458a(27) =178956942a(28) =357913912a(29) =715827852

External references