Number of permutations p() of 1..n+3 with centered difference p(i+1)-p(i-1) < 0 exactly twice.
A180880
Number of permutations p() of 1..n+3 with centered difference p(i+1)-p(i-1) < 0 exactly twice.
Terms
- a(0) =6a(1) =50a(2) =360a(3) =1960a(4) =10010a(5) =45738a(6) =203616a(7) =854700a(8) =3560172a(9) =14299428a(10) =57595824a(11) =226022940a(12) =895687650a(13) =3473777450a(14) =13672916400a(15) =52745436172a(16) =207268333844a(17) =798176908620
External references
- oeis: A180880