A127678 a(n) = numerator 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, 2, 2, 3, 5, 7, 17, 39, 131, 241, 1843, 33951, 475103, 66624833, 17107028693, 33453912854619, 1200873381252944089, 200445185648334612665809, 14036199771684615424002710560757

Offset

1,3

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]; Numerator[Nest[f, {1}, 20]] (* Ray Chandler, Feb 13 2007 *)

Crossrefs

Cf. A127679.

Sequence in context: A103597 A337745 A253853 * A199962 A114990 A241421

Adjacent sequences: A127675 A127676 A127677 * A127679 A127680 A127681

Keyword

easy,frac,nonn

Author

Leroy Quet, Jan 23 2007

Extensions

Extended by Ray Chandler, Feb 13 2007

Status

approved