OFFSET
1,1
COMMENTS
Conjecture: a(n+1)>=a(n)+42, with equality for infinitely many n,
namely those of the form a(n)=7^1+y^7, a(n+1)=7^2+y^7. - Robert Israel, May 09 2018
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
16433 is in this sequence because 16433 is prime and 7^2+3^7 = 16433.
33191 is in this sequence because 33191 is prime and 7^5+4^7 = 33191.
MAPLE
N:= 10^12: # to get all terms <= N
sort(select(isprime, [seq(seq(7^x+y^7, y=2..floor((N-7^x)^(1/7)), 2), x=1..floor(log[7](N)))])); # Robert Israel, May 09 2018
MATHEMATICA
f[x_, y_]:= 7^x + y^7; lst={}; Do[p=f[x, y]; If[PrimeQ[p], AppendTo[lst, p]], {y, 50}, {x, 50}]; Take[Union[lst], 30]
With[{nn=40}, Take[Sort[Select[7^#[[1]]+#[[2]]^7&/@Tuples[Range[nn], 2], PrimeQ]], nn]] (* Harvey P. Dale, May 28 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Dec 01 2014
STATUS
approved