A178220 Smallest number that appending to n-th prime gives another prime.

3, 1, 3, 1, 3, 1, 3, 1, 3, 3, 1, 3, 9, 1, 9, 23, 3, 3, 3, 9, 3, 7, 9, 23, 1, 3, 1, 11, 1, 11, 7, 9, 3, 9, 3, 1, 1, 7, 29, 3, 11, 1, 3, 1, 3, 3, 1, 7, 3, 3, 3, 3, 1, 11, 9, 3, 3, 1, 7, 9, 3, 9, 9, 9, 7, 21, 3, 1, 21, 1, 3, 3, 1, 3, 3, 3, 17, 19, 3, 1, 11, 1, 17, 7, 1, 51, 3, 37, 33, 7

Offset

1,1

Links

Table of n, a(n) for n=1..90.

Formula

a(n) = A030670(n) after deleting n-th prime.

Example

n=1: prime(1)=2, A030670(1)=23, after deleting 2 we get a(1)=3
n=2: prime(2)=3, A030670(2)=31, after deleting 3 we get a(2)=1

Mathematica

f[n_] := (k = 1; tsn = ToString[n]; While[a = ToExpression[tsn <> ToString[k]]; !PrimeQ[a], k++]; k);
Table[f[Prime[n]], {n, 1, 200}]

Crossrefs

Cf. A030670.

Sequence in context: A266875 A307193 A111742 * A334464 A316780 A338730

Adjacent sequences: A178217 A178218 A178219 * A178221 A178222 A178223

Keyword

nonn,base

Author

Zak Seidov, Dec 20 2010

Status

approved