A172125 - OEIS

A172125

a(n) = smallest prime of the form n*(n+1)*(n+2)...(n+k-1) - 1, or zero if no such a prime exists.

5, 5, 2, 3, 29, 5, 503, 7, 89, 109, 131, 11, 181, 13, 239, 271, 5813, 17, 379, 19, 461, 12143, 13799, 23, 53916693990528892723199999, 701, 657719, 811, 968330879, 29, 991, 31, 5339572260422399, 42839, 1259, 257256702743039, 54833, 37, 1559, 68879

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OFFSET

1,1

COMMENTS

A conjecture is that no term is zero.

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

a(1)=5 because 1-1=0 and 1*2-1=1 are not primes, but 1*2*3-1=5 is.

MATHEMATICA

a[n_] := Block[{}, For[s = n; k = 1, ! PrimeQ[s - 1], s *= n + k; k++ ]; s - 1]; Table[a[n], {n, 1, 100}]

CROSSREFS

Cf. A172130, A087564, A172133

Sequence in context: A319905 A319593 A335321 * A125642 A247039 A011335

Adjacent sequences: A172122 A172123 A172124 * A172126 A172127 A172128

KEYWORD

nonn

AUTHOR

Cheng Zhang (cz1(AT)rice.edu), Jan 26 2010, Mar 02 2010

STATUS

approved