login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A087554 a(n) = smallest number k >= n such that nk + 1 is a prime. 1
1, 2, 4, 4, 6, 6, 10, 9, 12, 10, 18, 13, 24, 14, 16, 16, 18, 21, 22, 20, 22, 28, 26, 24, 28, 26, 28, 34, 32, 33, 36, 36, 34, 37, 42, 36, 40, 39, 48, 40, 42, 46, 46, 47, 48, 51, 50, 54, 52, 51, 56, 55, 56, 54, 58, 56, 58, 61, 60, 67, 66, 63, 66, 67, 68, 66, 70, 75, 70, 79, 72, 79 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjectures: (1) k < 2n. (2) For every r, there exists a number S, nr < S < n(r+1) such that nS + 1 is prime.

LINKS

Table of n, a(n) for n=1..72.

MAPLE

for n from 1 to 120 do k := n: while(not isprime(n*k+1)) do k := k+1:od:a[n] := k:od:seq(a[l], l=1..120); # Sascha Kurz

CROSSREFS

Cf. A034693.

Sequence in context: A161765 A232091 A164798 * A281072 A226951 A251557

Adjacent sequences: A087551 A087552 A087553 * A087555 A087556 A087557

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Sep 13 2003

EXTENSIONS

Edited by Ray Chandler and Don Reble, Sep 16 2003

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 3 23:01 EST 2023. Contains 360045 sequences. (Running on oeis4.)