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A088140 a(n) = 1 if n is an odd prime otherwise a(n) = n. 7
2, 1, 4, 1, 6, 1, 8, 9, 10, 1, 12, 1, 14, 15, 16, 1, 18, 1, 20, 21, 22, 1, 24, 25, 26, 27, 28, 1, 30, 1, 32, 33, 34, 35, 36, 1, 38, 39, 40, 1, 42, 1, 44, 45, 46, 1, 48, 49, 50, 51, 52, 1, 54, 55, 56, 57, 58, 1, 60, 1, 62, 63, 64, 65, 66, 1, 68, 69, 70, 1, 72, 1, 74, 75, 76, 77, 78, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

From the factorial identity: n!=Product[Prime[i],{i,1,PrimePi[n]}]*Product[Composite[i],{i,1,n-PrimePi[n]}]

Tested to coincide with A005451 in the index range n=3..20000. [From R. J. Mathar, Sep 11 2008]

LINKS

Table of n, a(n) for n=2..79.

FORMULA

a(n) = Product[Composite[i], {i, 1, n-PrimePi[n]]/Product[Composite[i], {i, 1, n-1-PrimePi[n-1]]

MATHEMATICA

(* Composite Product*) p[n_]=n!/Product[Prime[i], {i, 2, PrimePi[n]}] digits=200 a0=Table[p[n]/p[n-1], {n, 2, digits}] (* Composites by sorting out ones and two*) Delete[Delete[Union[a0], 1], 1]

CROSSREFS

Cf. A002808.

Sequence in context: A317505 A137374 A131516 * A130758 A130892 A239871

Adjacent sequences:  A088137 A088138 A088139 * A088141 A088142 A088143

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Nov 04 2003

STATUS

approved

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Last modified October 1 08:39 EDT 2020. Contains 337442 sequences. (Running on oeis4.)