A338543 Numbers k such that 1 + Product_{i

1, 2, 8, 233, 431

Offset: 1

Author

Robert Israel, Nov 01 2020

Keywords

• nonn
• more

Comments

Numbers k such that A062347(k-1) == -1 (mod prime(k)).

Examples

			a(3)=8 is a term because 1 + 2*3*5*7*11*13*17 = 510511 is divisible by prime(8)=19.
		

Links

• Mathematics StackExchange, Is 510511 the smallest euclid number e_n that divides by the next prime p.

Crossrefs

Cf. A002110, A006862, A081618, A062347, A341805.

Programs

Maple

select(t -> 1+mul(ithprime(i),i=1..t-1) mod ithprime(t)=0, [$1..1000]);

PARI

isok(n) = ((1+vecprod(primes(n-1))) % prime(n)) == 0; \\ Michel Marcus, Nov 03 2020

Formula

a(n) = A081618(n)+1 for n >= 2.