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A084960
Initial prime of a prime chain of length n under the iteration x->5x+4.
8
2, 3, 5, 83, 263, 5333, 5333, 6714497, 42360737, 3757699889, 3757699889, 1431898413161, 5654774136689
OFFSET
1,1
COMMENTS
This is a special case of prime chains generated by f(x) = cx + d.
a(12) > 10551875981. [Donovan Johnson, Sep 27 2008]
LINKS
D. H. Lehmer, On certain chains of primes, Proc. London Math. Soc. (3) 14a 1965 183-186.
EXAMPLE
a(3) = 5 since 5, f(5) = 29 and f(29) = 149 are primes when f(x) = 5x+4.
MATHEMATICA
t[p_] := Block[{c=1, q = 5*p+4}, While[ PrimeQ@q, q = 5*q + 4; c++]; c]; a[n_] := Block[{p = 2}, While[t[p] < n, p = NextPrime@ p]; p]; Array[a, 8] (* Giovanni Resta, Mar 21 2017 *)
KEYWORD
nonn,more
AUTHOR
W. Edwin Clark, Jun 14 2003
EXTENSIONS
a(9) from Stefan Steinerberger, May 18 2007
a(10)-a(11) from Donovan Johnson, Sep 27 2008
a(12)-a(13) from Giovanni Resta, Mar 21 2017
STATUS
approved