A341805 Numbers k such that (product of first k primes)-1 is divisible by the (k+1)-th prime.

0, 2, 4, 9823712

Offset: 1

Author

Jeppe Stig Nielsen, Feb 20 2021

Keywords

• nonn
• hard
• more

Examples

			4 is a member because 2*3*5*7-1 (product of first 4 primes, minus one) is divisible by the 5th prime, 11.
9823712 is a member because 2*3*5*...*176078267-1 is divisible by 176078293, where 176078267 is the 9823712th prime.
		

Crossrefs

Cf. A079276, A081618, A338543, A341804, A341812.

Programs

PARI

isok(k) = ((vecprod(primes(k)) - 1) % prime(k+1)) == 0; \\ Michel Marcus, Mar 03 2021

Formula

a(n) = A000720(A341804(n)) - 1.