A090261 Beginning with a(1) = 1, choose a(n+1) so that concatenation a(n+1), a(n), a(n+1) is a new prime.

1, 3, 1, 9, 1, 17, 1, 21, 11, 13, 17, 7, 3, 11, 19, 9, 7, 111, 17, 13, 23, 1, 27, 17, 37, 3, 13, 33, 23, 7, 129, 11, 27, 43, 3, 17, 39, 17, 103, 3, 19, 17, 121, 117, 1, 29, 1, 39, 23, 9, 13, 51, 1, 41, 3, 37, 21, 13, 53, 1, 47, 1, 51, 7, 131, 7, 137, 19, 23, 13, 71, 7, 149, 1, 59, 3

Offset

1,2

Links

H. v. Eitzen, Table of n, a(n) for n = 1..10000.

Example

313, 131, 919, 191, 17117, 1171, 21121, etc. are primes.

Prog

(PARI) tp(n)=10^ceil(log(n+0.5)/log(10)); seen=Set([]); a=[1]; while(#a<100, n=a[ #a]; tn=tp(n); k=1; while(!isprime(z=(k*tn+n)*tp(k)+k) || setsearch(seen, z), k+=2); seen=setunion(seen, [z]); a=concat(a, k)); a \\ Hagen von Eitzen, Jun 21 2009

Crossrefs

Cf. A090260.

Sequence in context: A197259 A200006 A070894 * A303552 A130599 A157674

Adjacent sequences: A090258 A090259 A090260 * A090262 A090263 A090264

Keyword

base,nonn

Author

Amarnath Murthy, Nov 28 2003

Extensions

a(14) corrected and more terms added by Hagen von Eitzen, Jun 21 2009

Status

approved