Number of permutations of 1..n with i-7<=p(i)<=i+2.

Terms

a(0) =1a(1) =2a(2) =6a(3) =18a(4) =54a(5) =162a(6) =486a(7) =1458a(8) =4246a(9) =12355a(10) =36301a(11) =106872a(12) =314548a(13) =925540a(14) =2722708a(15) =8007988a(16) =23549956a(17) =69253444a(18) =203672180a(19) =599025237a(20) =1761804533a(21) =5181627922a(22) =15239550410a(23) =44820508518a(24) =131819918570a(25) =387690809990