A090478 a(1) = 1; for n>=1, a(n+1) is the least number such that the concatenation of a(n), n and a(n+1) is prime.

1, 3, 17, 3, 7, 1, 3, 3, 3, 7, 3, 9, 7, 17, 27, 17, 7, 7, 7, 3, 3, 7, 9, 9, 1, 9, 23, 9, 1, 1, 1, 9, 3, 1, 11, 1, 1, 3, 9, 1, 9, 3, 11, 7, 11, 47, 19, 1, 1, 3, 23, 11, 7, 7, 1, 3, 17, 3, 1, 7, 3, 3, 3, 1, 11, 7, 9, 7, 1, 3, 1, 17, 9, 3, 23, 3, 1, 7, 9, 1, 1, 1, 3, 3, 7, 3, 3, 7, 3, 17, 3, 1, 11, 3, 3, 11

Offset

1,2

Links

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

Example

113, 3217, 1733 etc. are primes. 3217 is the prime obtained by placing 2 in the second gap.

Mathematica

nxt[{n_, a_}]:=Module[{k=1, c=a*10^IntegerLength[n]+n}, While[!PrimeQ[c*10^IntegerLength[k]+k], k++]; {n+1, k}]; NestList[nxt, {1, 1}, 100][[;; , 2]] (* Harvey P. Dale, Jul 11 2025 *)

Crossrefs

Sequence in context: A285740 A174506 A109216 * A231785 A195421 A140446

Adjacent sequences: A090475 A090476 A090477 * A090479 A090480 A090481

Keyword

base,nonn

Author

Amarnath Murthy, Dec 02 2003

Extensions

More terms from David Wasserman, Nov 16 2005

Status

approved