A007975 Number of permutations that are 3 "block reversals" away from 12...n.

2, 55, 389, 1563, 4642, 11407, 24600, 48204, 87758, 150707, 246787, 388445, 591294, 874603, 1261822, 1781142, 2466090, 3356159, 4497473, 5943487, 7755722, 10004535, 12769924, 16142368, 20223702, 25128027, 30982655, 37929089, 46124038, 55740467, 66968682, 80017450, 95115154, 112510983, 132476157, 155305187, 181317170

Offset: 4

Author

J. H. Conway

Keywords

• nonn

Crossrefs

Cf. A007972, A007973, A007974.

Cf. A000124, A228396, A228397.

Column k=3 of A300003.

Formula

a(n) = A228397(n) - A228396(n). See C. Homberger links from A228396. - Martin Fuller, Mar 31 2025

Extensions

More terms from Sean A. Irvine, Feb 22 2018

a(34) onwards from Martin Fuller, Mar 31 2025