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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A085747 Least positive k such that n! + k is a semiprime. 7
3, 2, 3, 1, 1, 1, 1, 1, 5, 1, 3, 17, 1, 1, 7, 2, 3, 23, 1, 1, 11, 29, 3, 1, 1, 1, 37, 1, 41, 2, 19, 11, 11, 1, 7, 3, 41, 1, 13, 127, 47, 59, 2, 37, 5, 37, 59, 1, 2, 73, 59, 79, 73, 1, 1, 61, 118, 37, 1, 61, 31, 37, 43, 7, 83, 71, 19, 7, 103, 19, 1, 107, 37, 167, 1, 103, 3, 73, 109, 97 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(104) >= 227, a(105)=137. - Max Alekseyev, Nov 18 2014

a(n) = 1 iff n in A078778.

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..103 (a(100) from Sean A. Irvine)

Dario Alejandro Alpern, Factorization using the Elliptic Curve Method

factordb, Status of 104!+227.

Hisanori Mishima, Factorization of n! + 1 (n = 1 to 100)

MATHEMATICA

Table[SelectFirst[Range@ 1000, PrimeOmega[n! + #] == 2 &], {n, 40}] (* Michael De Vlieger, Mar 08 2016, Version 10 *)

PROG

(PARI) a(n) = {k = 1; while (bigomega(n!+k) != 2, k++); k; } \\ Michel Marcus, Mar 08 2016

(MAGMA) m:=1; sol:=[]; for n in [1..40] do k:=1; while &+[d[2]: d in Factorization(Factorial(n)+k)] ne 2 do k:=k+1; end while; sol[m]:=k; m:=m+1; end for; sol; // Marius A. Burtea, Aug 24 2019

CROSSREFS

Cf. A089538, A089539, A089540, A089541.

Sequence in context: A103497 A191390 A309698 * A106693 A107335 A200223

Adjacent sequences:  A085744 A085745 A085746 * A085748 A085749 A085750

KEYWORD

nonn,hard

AUTHOR

Jason Earls, Jul 21 2003

EXTENSIONS

Extended by Robert G. Wilson v, Jul 27 2003

a(55) from Ray Chandler, Nov 09 2003

a(56)-a(80) from Sean A. Irvine, Mar 29 2010

STATUS

approved

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 October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)