A121826 -id:A121826 - cp's OEIS frontend

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

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Jason Earls, Aug 28 2006

nonn
base

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

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

Cf. A013632, A020338, A121826, A151800.

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

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

cp's OEIS Frontend

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

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