

A109904


a(1)= 5. a(n+1) = greatest prime of the form k*{a(n)k} +1. The least prime occurs for k = 1 and a(n+1) = a(n) in that case if no other value of k gives a prime then the sequence terminates.


5




OFFSET

0,1


COMMENTS

For the first five terms k = INT[a(n)/2]. k can take values from 1 to INT[a(n)/2]. It is conjectured that at least one value of k, 2= < k < INT[a(n)/2] gives a prime and the sequence is infinite.


LINKS

Table of n, a(n) for n=0..9.


EXAMPLE

a(2)= 2*3 +1=7, a(3) = 3*4 +1 =13.


PROG

(PARI) { b(n)=forstep(k=n\2, 1, 1, if(isprime(k*(nk)+1), return(k*(nk)+1))); return(0) } s=5; while(1, print1(s, " "); s=b(s)) (Alekseyev)


CROSSREFS

Cf. A109905, A026728.
Sequence in context: A063446 A064600 A174874 * A077781 A102872 A102873
Adjacent sequences: A109901 A109902 A109903 * A109905 A109906 A109907


KEYWORD

nonn


AUTHOR

Amarnath Murthy, Jul 15 2005


EXTENSIONS

More terms from Max Alekseyev, Oct 04 2005


STATUS

approved



