OFFSET
1,1
COMMENTS
Each term is a prime or one less than a prime.
Each even term is twice an odd prime (except for a(1)=2).
Each prime term is of the form 2p-1 where p is prime.
FORMULA
Conjecture: a(n) ~ 2*n.
EXAMPLE
For n=5, a(5) = 13 since the two numbers 13 and 14=2*7 both have a prime factor > n.
PROG
(PARI) gpf(n) = vecmax(factor(n)[, 1]); \\ A006530
a(n) = my(k=2); while(!((gpf(k)>n) && (gpf(k+1)>n)), k++); k; \\ Michel Marcus, Jan 10 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Garrison, Jan 02 2023
STATUS
approved