A070916 a(1)=1, a(n) is the smallest integer >= a(n-1) such that a(n)*a(n-1) - 1 is prime.

1, 3, 4, 5, 6, 7, 12, 14, 16, 17, 22, 26, 27, 30, 31, 32, 34, 36, 38, 39, 40, 44, 45, 46, 47, 60, 61, 72, 75, 78, 81, 84, 87, 90, 93, 94, 95, 102, 104, 115, 116, 118, 120, 121, 132, 142, 146, 154, 155, 156, 164, 165, 182, 184, 185, 190, 192, 202, 206, 207, 216, 218

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Formula

Conjecture: lim_{n -> infinity} a(n)/(n*log(n)) = C = 1.075... .

Mathematica

si[n_]:=Module[{k=n}, While[!PrimeQ[k*n-1], k++]; k]; NestList[si, 1, 70] (* Harvey P. Dale, Jul 25 2013 *)

Prog

(PARI) s=1; for(n=1, 100, t=s; while(isprime(s*t-1)==0, s++); print1(s, ", "))

Crossrefs

Sequence in context: A052002 A247636 A361267 * A078305 A235324 A330373

Adjacent sequences: A070913 A070914 A070915 * A070917 A070918 A070919

Keyword

easy,nonn

Author

Benoit Cloitre, May 20 2002

Status

approved