A061309 - OEIS

A061309

a(n) is the smallest number required to make the concatenation of a(n) and 2n+1 a prime, or -1 if no such number exists.

1, 0, 0, 0, 1, 0, 0, -1, 0, 0, 4, 0, -1, 1, 0, 0, 2, -1, 0, 1, 0, 0, -1, 0, 1, 1, 0, -1, 1, 0, 0, 1, -1, 0, 2, 0, 0, -1, 2, 0, 1, 0, -1, 4, 0, 1, 1, -1, 0, 1, 0, 0, -1, 0, 0, 2, 0, -1, 1, 3, 3, 1, -1, 0, 1, 0, 4, -1, 0, 0, 2, 2, -1, 5, 0, 0, 1, -1, 0, 4, 2, 0, -1, 0, 3, 1, 0, -1, 4, 0, 0, 13

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OFFSET

0,11

COMMENTS

a(0) = 0 for a prime.

LINKS

Table of n, a(n) for n=0..91.

EXAMPLE

a(9) = 0 as 19 itself is a prime; a(10) = 4 as 421 is a prime but 121, 221, 321 are not.

CROSSREFS

Sequence in context: A068346 A348304 A006838 * A263655 A329078 A059064

Adjacent sequences: A061306 A061307 A061308 * A061310 A061311 A061312