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

Author

Zak Seidov, Dec 20 2010

Keywords

• nonn
• base

Examples

			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
		

Crossrefs

Cf. A030670.

Programs

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}]

Formula

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