login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A056110 Highest proper factor of n!-1, or a(n)=1 if n!-1 is not composite. 4

%I

%S 1,1,1,17,1,1,1753,32989,125131,3070523,1,3593203,1,76922021647,

%T 6880233439,18720390952421,108514808571661,186286524362683,

%U 19499250680671,2221345311813453913,10311933282363373211,498390560021687969,991459181683,104102080827724738147651,19739193437746837432529

%N Highest proper factor of n!-1, or a(n)=1 if n!-1 is not composite.

%H Hisanori Mishima, <a href="http://www.asahi-net.or.jp/~KC2H-MSM/mathland/matha1/matha105.htm">Factorizations of many number sequences: n! - 1 (n = 1 to 100)</a>.

%H R. G. Wilson v, <a href="/A038507/a038507.txt">Explicit factorizations</a>

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

%t 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 *)

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

%Y Cf. A002582.

%K nonn

%O 2,4

%A _Henry Bottomley_, Jun 12 2000

%E Edited and extended by _M. F. Hasler_, Oct 31 2012

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 19 16:38 EST 2019. Contains 320311 sequences. (Running on oeis4.)