A099081
Numbers k such that 1.2. ... .k-1.k + 1 is prime (where dot between numbers means concatenation).
Original entry on oeis.org
1, 2, 6, 30, 88
Offset: 1
6 is in the sequence because 123456+1 is prime.
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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 *)
A099083
Numbers k such that 1.2. ... .k-1.k - 2 is prime (where dot between numbers means concatenation).
Original entry on oeis.org
5, 31, 103, 111, 119, 201
Offset: 1
31 is in the sequence because 12345678910111213141516171819202122232425262728293031 - 2 is prime.
A099084
Numbers k such that 1.2. ... .k-1.k + 4 is a prime (dot between numbers means concatenation).
Original entry on oeis.org
1, 3, 27, 663, 6919
Offset: 1
27 is in the sequence because 123456789101112131415161718192021222324252627 + 4 is a prime.
Showing 1-3 of 3 results.
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