A086125 Values of n such that f(n) is a prime, where f(1) = 1, f(n) = prime(n)*f(n-1) + 2.

2, 4, 8, 15, 31, 128, 163

Offset

1,1

Comments

No additional terms up to n = 1000. - Harvey P. Dale, Feb 02 2019

Links

Table of n, a(n) for n=1..7.

Mathematica

f[1]=1; f[x_] := f[x] = Prime[x]*f[x - 1] + 2; Do[ If[ PrimeQ[ f[n]], Print[n]], {n, 1, 1900}]
nxt[{n_, a_}]:={n+1, a*Prime[n+1]+2}; Select[NestList[nxt, {1, 1}, 200], PrimeQ[ #[[2]]]&][[All, 1]] (* Harvey P. Dale, Feb 02 2019 *)

Crossrefs

The primes are in A086124.

Cf. A000668, A076481, A086122, A086123, A086124.

Sequence in context: A092603 A298533 A259805 * A227236 A061030 A036661

Adjacent sequences: A086122 A086123 A086124 * A086126 A086127 A086128

Keyword

more,nonn

Author

Labos Elemer, Jul 23 2003

Extensions

Edited by Robert G. Wilson v, Jul 25 2003

Status

approved