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A338543
Numbers k such that 1 + Product_{i<k} prime(i) is divisible by prime(k).
2
1, 2, 8, 233, 431
OFFSET
1,2
COMMENTS
Numbers k such that A062347(k-1) == -1 (mod prime(k)).
FORMULA
a(n) = A081618(n)+1 for n >= 2.
EXAMPLE
a(3)=8 is a term because 1 + 2*3*5*7*11*13*17 = 510511 is divisible by prime(8)=19.
MAPLE
select(t -> 1+mul(ithprime(i), i=1..t-1) mod ithprime(t)=0, [$1..1000]);
PROG
(PARI) isok(n) = ((1+vecprod(primes(n-1))) % prime(n)) == 0; \\ Michel Marcus, Nov 03 2020
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Israel, Nov 01 2020
STATUS
approved