A178220 - OEIS

%I #13 Mar 30 2012 17:26:35

%S 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,

%T 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,

%U 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

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

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

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

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

%t f[n_] := (k = 1; tsn = ToString[n]; While[a = ToExpression[tsn <> ToString[k]]; !PrimeQ[a], k++]; k);

%t Table[f[Prime[n]], {n, 1, 200}]

%Y Cf. A030670.

%K nonn,base

%O 1,1

%A _Zak Seidov_, Dec 20 2010