A115587 a(n) = denominator of b(n), where b(1) = 1, b(n+1) = Sum_{k=1..n} b(k)^((-1)^(n-k)).

1, 1, 1, 1, 2, 4, 52, 559, 2023580, 639046564, 73885083538076135, 13974134129149036419614094980, 9508386737708519692119190558953351866716894940, 167312950453078829361896561420857502596441619698513063185995475418519527687170

Offset

1,5

Links

Michael De Vlieger, Table of n, a(n) for n = 1..19

Example

{b(n)} begins 1, 1, 2, 4, 13/2, 43/4, ...
So b(7) = 1 + 1 + 1/2 + 4 + 2/13 + 43/4 = 905/52 and therefore a(7) = 52.

Maple

b[1]:=1: for n from 1 to 14 do b[n+1]:=sum(b[k]^((-1)^(n-k)), k=1..n): a[n]:=denom(b[n]) od: seq(a[n], n=1..14); # Emeric Deutsch, Mar 30 2006

Mathematica

b[n_] := b[n] = If[n == 1, 1, Sum[b[k]^((-1)^(n - k - 1)), {k, n - 1}]]; Array[Denominator@ b@ # &, 14] (* Michael De Vlieger, Sep 30 2017 *)

Crossrefs

Cf. A115600, A115601, A115602.

Sequence in context: A085325 A082661 A205616 * A018337 A092389 A341733

Adjacent sequences: A115584 A115585 A115586 * A115588 A115589 A115590

Keyword

frac,nonn

Author

Leroy Quet, Mar 13 2006

Extensions

More terms from Emeric Deutsch, Mar 30 2006

Status

approved