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A092914 a(n) = (n-1)*(n-2)*...*(n-r) with the least value of r so that n divides a(n). 3
60, 0, 840, 20160, 15120, 0, 7920, 0, 8648640, 240240, 3603600, 0, 8910720, 0, 1395360, 390700800, 14079294028800, 0, 212520, 7117005772800, 32382376266240000, 1133836704000, 4475671200, 0, 14250600, 0, 318073392000 (list; graph; refs; listen; history; text; internal format)
OFFSET

6,1

COMMENTS

Analogous to the Kempner sequence A002034 where one goes forwards instead of backwards.

Least multiple of n of the form (n-1)!/k! if n is composite, 0 if n is prime.

a(1) = ... = a(5) = 0, so offset is set to 6. In fact 4 is the only composite n such that a(n) = 0. a(2p) = (2p-1)!/(p-1)! if p is a prime.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 6..733

EXAMPLE

9 divides 8*7*6*5*4*3 = 20160 but 9 does not divide 8*7*6*5*4, so a(9) = 20160.

MATHEMATICA

Table[SelectFirst[FoldList[Times, Range[n-1, 0, -1]], Divisible[#, n]&], {n, 6, 40}] (* Harvey P. Dale, Jul 29 2015 *)

PROG

(PARI) m=32; for(n=6, m, r=1; p=n-r; while(r<=n&&p%n>0, r++; p=p*(n-r)); print1(p, ", "))

CROSSREFS

Cf. A092915, A092916.

Sequence in context: A093403 A087535 A058931 * A022083 A174675 A016532

Adjacent sequences:  A092911 A092912 A092913 * A092915 A092916 A092917

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Mar 16 2004

EXTENSIONS

Edited and extended by Klaus Brockhaus, Mar 17 2004

STATUS

approved

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Last modified April 5 13:14 EDT 2020. Contains 333241 sequences. (Running on oeis4.)