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

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]]

Crossrefs

Cf. A085063, A092945, A085063, A120223, A120225.

Sequence in context: A168275 A325968 A325818 * A210471 A183107 A132009

Adjacent sequences: A120221 A120222 A120223 * A120225 A120226 A120227

Keyword

nonn

Author

Zak Seidov, Jun 10 2006

Status

approved