A072999 a(n+1) is the smallest prime>a(n) such that a(n+1) == a(n-1) (mod a(n)).

2, 3, 5, 13, 31, 137, 853, 6961, 28697, 179143, 6836131, 68540453, 966402473, 15530980021, 94152282599, 203835545219, 2540178825227, 61168127350667, 6119352913891927, 220357873027460039, 16312601956945934813

Offset

0,1

Links

T. D. Noe, Table of n, a(n) for n=0..100

Example

After 3,5, one can't have composite 8, so keep adding 5 until you reach 13. After 5,13, one can't have composite 18, so keep adding 13 until you reach 31.

Mathematica

nxt[{a_, b_}]:=Module[{c=a+b}, While[CompositeQ[c], c=c+b]; {b, c}]; NestList[ nxt, {2, 3}, 20][[All, 1]] (* Harvey P. Dale, Aug 01 2017 *)

Prog

(PARI) l=2; h=3; print1("2, 3, "); while(l<2^128, t=l+h; while(!isprime(t), t+=h); print1(t, ", "); l=h; h=t)

Crossrefs

Cf. A073680, A072535.

Cf. A083698: partial fraction having these primes as numerators or denominators.

Sequence in context: A041519 A355512 A060434 * A175093 A342180 A345076

Adjacent sequences: A072996 A072997 A072998 * A073000 A073001 A073002

Keyword

nonn

Author

Phil Carmody, Aug 15 2002

Status

approved