Number of set partitions of [n] such that seven is a multiple of each block size.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =9a(9) =37a(10) =121a(11) =331a(12) =793a(13) =1717a(14) =5149a(15) =32176a(16) =217361a(17) =1186329a(18) =5282785a(19) =20004037a(20) =66589681a(21) =266164921a(22) =2012163385a(23) =18230119678a(24) =137986473241a(25) =849028203101