A084402 - OEIS

A084402

n-th partial product - 1 is a prime, where a(n) > 1.

3, 2, 2, 2, 2, 4, 2, 3, 6, 4, 5, 5, 5, 10, 4, 3, 5, 8, 22, 13, 14, 2, 5, 5, 2, 20, 9, 9, 24, 5, 26, 15, 14, 25, 25, 4, 9, 30, 9, 21, 12, 11, 10, 2, 40, 19, 8, 13, 11, 50, 3, 25, 25, 8, 5, 25, 46, 19, 47, 54, 9, 13, 14, 43, 4, 24, 28, 16, 33, 25, 152, 2, 11, 22, 6, 78, 87, 7, 10, 21, 77, 23

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OFFSET

1,1

COMMENTS

a(n) exists for each n by Dirichlet's theorem. - Charles R Greathouse IV, Oct 31 2014

Same as A036013 for n > 4. - Georg Fischer, Oct 19 2018

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..586 (terms 1..300 from Georg Fischer)

EXAMPLE

3-1 = 2, 3*2-1 = 5, 3*2*2 -1 = 11, etc. are primes.

PROG

(PARI) lista(nn) = {v = vector(nn); for (n=1, nn, v[n] = 2; while (! isprime(prod(i=1, n, v[i])-1), v[n]++); print1(v[n], ", "); ); } \\ Michel Marcus, Oct 31 2014

(PARI) first(n) = my(res=vector(n), pp=1, t); for(i = 1, n, t = 2; while(!isprime(pp * t - 1), t++); pp *= t; res[i]=t); res \\ David A. Corneth, Oct 19 2018

CROSSREFS

Cf. A036013, A084401.

Sequence in context: A272893 A037199 A145376 * A127599 A207384 A085034

Adjacent sequences: A084399 A084400 A084401 * A084403 A084404 A084405

KEYWORD

nonn

AUTHOR

Amarnath Murthy, May 31 2003

EXTENSIONS

More terms from David Wasserman, Dec 22 2004

STATUS

approved