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A099081 Numbers n such that 1.2. ... .n-1.n + 1 is prime (where dot between numbers means concatenation). 4
1, 2, 6, 30, 88 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

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

MATHEMATICA

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 *)

CROSSREFS

Cf. A099082, A099083.

Sequence in context: A328417 A290760 A088857 * A051844 A335396 A034501

Adjacent sequences:  A099078 A099079 A099080 * A099082 A099083 A099084

KEYWORD

base,more,nonn

AUTHOR

Farideh Firoozbakht, Oct 23 2004

STATUS

approved

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Last modified August 10 19:52 EDT 2020. Contains 336381 sequences. (Running on oeis4.)