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A099081 Numbers n such that 1.2. ... .n-1.n + 1 is prime (where dot between numbers means concatenation). 4

%I #5 Jul 29 2015 01:15:01

%S 1,2,6,30,88

%N Numbers n such that 1.2. ... .n-1.n + 1 is prime (where dot between numbers means concatenation).

%e 6 is in the sequence because 123456+1 is prime.

%t f[n_] := Block[{p = 0, k = 1}, While[k <= n, p = 10^Floor[ Log[10, k] + 1]p + k; k++ ]; PrimeQ[p + 1]]; Do[ If[ f[n], Print[n]], {n, 1000}] (* _Robert G. Wilson v_, Nov 01 2004 *)

%Y Cf. A099082, A099083.

%K base,more,nonn

%O 1,2

%A _Farideh Firoozbakht_, Oct 23 2004

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Last modified March 29 02:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)