A121837 Least positive j such that Product_{k=1..n} D(k) + j is prime, where D() are the doublets, A020338.

2, 9, 7, 7, 17, 7, 29, 17, 19, 23, 23, 13, 29, 79, 19, 89, 97, 53, 43, 347, 127, 127, 149, 29, 167, 331, 379, 61, 59, 167, 199, 557, 107, 113, 43, 191, 439, 41, 263, 227, 109, 71, 227, 137, 149, 409, 271, 53, 157, 79, 503, 103, 461, 137, 587, 233, 491, 73, 367, 233, 449

Offset

1,1

Comments

Is every term for n > 2 always prime?

a(159) = 1. - Michel Marcus, Jan 07 2021

a(n) = 1 for n = 245 and 702 (using ispseudoprime() in PARI). - Michel Marcus, Jan 08 2021

Links

Michel Marcus, Table of n, a(n) for n = 1..200

Formula

a(n) = A013632(A121826(n)). - Michel Marcus, Jan 07 2021

Prog

(PARI) D(n) = eval(Str(n, n)); \\ A020338
f(n) = prod(k=1, n, D(k)); \\ A121826
a(n) = my(q=f(n)); nextprime(q+1) - q; \\ Michel Marcus, Jan 07 2021

Crossrefs

Cf. A013632, A020338, A121826, A151800.

Sequence in context: A021340 A241753 A157350 * A160439 A245287 A254595

Adjacent sequences: A121834 A121835 A121836 * A121838 A121839 A121840

Keyword

nonn,base

Author

Jason Earls, Aug 28 2006

Status

approved