A127679 a(n) = denominator of b(n), where b(1) = 1, b(n+1) = (sum{k=1 to n} b(k))/product{j=1 to n} b(j).

1, 1, 1, 1, 2, 4, 6, 15, 35, 119, 221, 1703, 31571, 444163, 62571693, 16130221953, 31653658032799, 1139752929797333269, 190765682365696256860989, 13391304481955883169111997465697

Offset

1,5

Links

Table of n, a(n) for n=1..20.

Formula

For n >= 4, b(n) = 1 +(b(n-1)-1)/b(n-2).

Mathematica

f[l_List] := Append[l, Plus @@ l/Times @@ l]; Denominator[Nest[f, {1}, 20]] (* Ray Chandler, Feb 13 2007 *)

Crossrefs

Cf. A127678.

Sequence in context: A227902 A217525 A295615 * A049022 A209867 A136033

Adjacent sequences: A127676 A127677 A127678 * A127680 A127681 A127682

Keyword

easy,frac,nonn

Author

Leroy Quet, Jan 23 2007

Extensions

Extended by Ray Chandler, Feb 13 2007

Status

approved