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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..5.

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

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

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

Sequence in context: A013344 A091503 A009588 * A125264 A028985 A067583

Adjacent sequences:  A338540 A338541 A338542 * A338544 A338545 A338546

KEYWORD

nonn,more

AUTHOR

Robert Israel, Nov 01 2020

STATUS

approved

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Last modified April 15 06:12 EDT 2021. Contains 342975 sequences. (Running on oeis4.)