A181608 Smallest positive number such that, enclosed by prime(n) gives a prime, or zero if no such prime exists.

0, 1, 0, 2, 3, 3, 1, 2, 6, 1, 2, 3, 1, 5, 1, 3, 1, 2, 5, 1, 6, 2, 3, 1, 3, 12, 15, 4, 3, 1, 3, 1, 1, 8, 6, 3, 14, 5, 3, 6, 3, 26, 7, 2, 3, 21, 3, 3, 15, 9, 7, 1, 3, 16, 6, 1, 7, 15, 5, 9, 2, 4, 12, 12, 5, 4, 5, 8, 4, 3, 13, 1, 2, 2, 6, 6, 1, 6, 4, 3, 4, 2, 9, 5, 5, 1, 10, 6, 1, 3, 1, 6, 5, 9, 2, 3, 1, 6, 3, 5, 2, 4, 7, 4, 14, 3, 3, 3, 3

Offset

1,4

Links

Alois P. Heinz, Table of n, a(n) for n = 1..10000

Example

a(5)=3 since prime(5)=11 and 11311 is prime.

Maple

read("transforms") ;
A181608 := proc(n) local p, k, l ; if n= 1 or n = 3 then return 0 ; end if; p := ithprime(n) ; for k from 0 do l := digcat2(digcat2(p, k), p) ; if isprime(%) then return k; end if; end do: end proc: # R. J. Mathar, Jan 30 2011

Mathematica

Table[p = Prime[n]; If[Mod[10, p] == 0, 0, k = 0; While[!PrimeQ[FromDigits[Join[IntegerDigits[p], IntegerDigits[k], IntegerDigits[p]]]], k++]; k], {n, 109}]

Crossrefs

Cf. A070278, A071234, A154270.

Sequence in context: A294101 A051911 A106595 * A272873 A295634 A317665

Adjacent sequences: A181605 A181606 A181607 * A181609 A181610 A181611

Keyword

nonn,base

Author

Carmine Suriano, Jan 30 2011

Status

approved