A120224 - OEIS

A120224

a(n) is the minimal number k>=n such that n+k and n*k+1 are primes.

1, 3, 4, 7, 6, 7, 10, 9, 14, 13, 18, 19, 24, 15, 16, 21, 24, 29, 22, 21, 22, 31, 30, 43, 28, 33, 34, 39, 32, 41, 36, 39, 34, 37, 66, 43, 60, 41, 50, 43, 42, 55, 46, 53, 52, 51, 50, 59, 52, 51, 56, 55, 56, 55, 58, 75, 74, 69, 68, 67, 66, 75, 74, 67, 86, 83, 70, 89, 70, 79, 102, 79

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OFFSET

1,2

COMMENTS

Differs from A120225 in the first term.

LINKS

Table of n, a(n) for n=1..72.

EXAMPLE

a(3)=4 because 3+4=7 and 3*4+1=13 are prime;

a(8)=9 because 8+9=17 and 8*9+1=73 are prime,

MATHEMATICA

Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]; Break[]], {x, n, 1000}], {n, 120}]][[2, 1]]