A334776 Total number of peaks in all permutations of 2 indistinguishable copies of 1..n.

0, 3, 105, 4620, 283500, 23700600, 2610808200, 367783416000, 64607286744000, 13859305059600000, 3567385122341040000, 1085582734152396480000, 385634331725066424000000, 158175715893528308976000000, 74203019661816956710800000000, 39481403043334753112451840000000

Offset: 1

Author

Andrew Howroyd, May 12 2020

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A000680, A334774, A334775, A334777.

Programs

PARI

\\ PeaksBySig defined in A334774.
a(n)={my(u=PeaksBySig(vector(n,i,2), [0..n-1])); sum(k=1, #u, (k-1)*u[k])}

Formula

a(n) = Sum_{k=1..n} (k-1)*A334774(n,k).

a(n) = A334777(n) - A000680(n).