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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 December 10 08:26 EST 2023. Contains 367701 sequences. (Running on oeis4.)