

A109904


a(1) = 5. a(n+1) is the 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.


6




OFFSET

1,1


COMMENTS

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


LINKS



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)) \\ Max Alekseyev, Oct 04 2005


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



