Let b(n) be the number of permutations {c_1..c_n} of {1..n} for which c_1 - c_2 + ... + (-1)^(n-1)*c_n are pentagonal numbers (A000326). Then a(n) = b(n)/A010551(n).
A294812
Let b(n) be the number of permutations {c_1..c_n} of {1..n} for which c_1 - c_2 + ... + (-1)^(n-1)*c_n are pentagonal numbers (A000326). Then a(n) = b(n)/A010551(n).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =5a(6) =6a(7) =10a(8) =23a(9) =38a(10) =70a(11) =110a(12) =196a(13) =346a(14) =759a(15) =1250a(16) =2313a(17) =3982a(18) =8433a(19) =14520a(20) =29437a(21) =50466a(22) =102830a(23) =179587a(24) =376439a(25) =654374a(26) =1343540a(27) =2352149a(28) =4916286a(29) =8654120
External references
- oeis: A294812