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A056110 Highest proper factor of n!-1, or a(n)=1 if n!-1 is not composite. 4
1, 1, 1, 17, 1, 1, 1753, 32989, 125131, 3070523, 1, 3593203, 1, 76922021647, 6880233439, 18720390952421, 108514808571661, 186286524362683, 19499250680671, 2221345311813453913, 10311933282363373211, 498390560021687969, 991459181683, 104102080827724738147651, 19739193437746837432529 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,4

LINKS

Table of n, a(n) for n=2..26.

Hisanori Mishima, Factorizations of many number sequences: n! - 1 (n = 1 to 100).

R. G. Wilson v, Explicit factorizations

FORMULA

a(n) = A033312(n)/A054415(n)

MATHEMATICA

pf[n_]:=Module[{c=n!-1}, If[PrimeQ[c], 1, c/FactorInteger[c][[1, 1]]]]; Array[pf, 30, 2] (* Harvey P. Dale, Dec 13 2012 *)

PROG

(PARI) A056110(n)={n=factor(n!-1); if(norml2(n[, 2])>1, factorback(n)/n[1, 1], 1)} \\ - M. F. Hasler, Oct 31 2012

CROSSREFS

Cf. A002582.

Sequence in context: A156581 A015143 A172196 * A040296 A040297 A239866

Adjacent sequences:  A056107 A056108 A056109 * A056111 A056112 A056113

KEYWORD

nonn

AUTHOR

Henry Bottomley, Jun 12 2000

EXTENSIONS

Edited and extended by M. F. Hasler, Oct 31 2012

STATUS

approved

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Last modified January 23 00:56 EST 2019. Contains 319365 sequences. (Running on oeis4.)