

A128509


Initial prime, greater than 7, of a prime chain of length n under the iteration x > 2x7.


1



11, 13, 13, 367, 4987, 9697, 78007, 13356127, 13356127, 6753069187, 218617084627, 35679817649197, 92975416840027
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OFFSET

1,1


COMMENTS

From the definition we see that the sequence is monotonic (but not strictly) increasing. The sequence is a generalized Cunningham chain.  Stefan Steinerberger, May 12 2007


LINKS



EXAMPLE

a(2) = 13 because 13, 13*27=19 and 19*27=31 are primes.


MATHEMATICA

k = 5; For[n = 2, n <= 10, n++, While[Union[PrimeQ[NestList[2#  7 &, Prime[k], n]], PrimeQ[NestList[2#  7 &, Prime[k], n]]] != {True}, k++ ]; Print[Prime[k]]] (* Stefan Steinerberger, May 12 2007 *)


CROSSREFS



KEYWORD

nonn,more


AUTHOR



EXTENSIONS



STATUS

approved



