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A128045 a(n) = denominator of b(n), where b(1) = 1, b(n) = sum{k=1 to n-1} b(n-k) * H(k); H(k) = sum{j=1 to k} 1/j, the k-th harmonic number. 2
1, 1, 2, 6, 2, 5, 360, 2520, 1680, 15120, 2700, 11880, 9979200, 8648640, 18345600, 2476656000, 27243216000, 714714000, 427508928000, 1160381376000, 1055947052160000, 22174888095360000, 38718058579200, 141031842336000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..24.

MATHEMATICA

f[l_List] := Block[{n = Length[l] + 1}, Append[l, Sum[l[[n - k]]*HarmonicNumber[k], {k, n - 1}]]]; Denominator[Nest[f, {1}, 24]] (*Chandler*)

CROSSREFS

Cf. A128044.

Sequence in context: A268766 A214775 A196201 * A011325 A010696 A021796

Adjacent sequences:  A128042 A128043 A128044 * A128046 A128047 A128048

KEYWORD

nonn,frac

AUTHOR

Leroy Quet, Feb 11 2007

EXTENSIONS

Extended by Ray Chandler, Feb 12 2007

STATUS

approved

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Last modified May 24 20:53 EDT 2019. Contains 323534 sequences. (Running on oeis4.)