Triangle read by rows: T(n,k) is the number of set partitions of the set {1,2,...,n} containing k blocks of size 2 (0 <= k <= floor(n/2)).

A124498

Triangle read by rows: T(n,k) is the number of set partitions of the set {1,2,...,n} containing k blocks of size 2 (0 <= k <= floor(n/2)).

Terms

    a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =6a(7) =6a(8) =3a(9) =17a(10) =20a(11) =15a(12) =53a(13) =90a(14) =45a(15) =15a(16) =205a(17) =357a(18) =210a(19) =105a(20) =871a(21) =1484a(22) =1260a(23) =420a(24) =105a(25) =3876a(26) =7380a(27) =6426a(28) =2520a(29) =945

External references