OFFSET
1,1
COMMENTS
Primes of form x^7 + y^7 + z^7 where x, y, z > 0.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
3 = 1^7 + 1^7 + 1^7;
257 = 1^7 + 2^7 + 2^7;
82499 = 3^7 + 3^7 + 5^7, etc.
MAPLE
N:= 10^9: # to get all terms <= N
Res:= {}:
for x from 1 to floor(N^(1/7)) do
for y from 1 to min(x, floor((N-x^7)^(1/7))) do
for z from 1 to min(y, floor((N-x^7-y^7)^(1/7))) do
p:= x^7 + y^7 + z^7;
if isprime(p) then Res:= Res union {p} fi
od od od:
sort(convert(Res, list)); # Robert Israel, Feb 26 2017
MATHEMATICA
nn = 14; Select[Union[Plus @@@ (Tuples[Range[nn], {3}]^7)], # <= nn^7 && PrimeQ[#] &]
PROG
(PARI) list(lim)=my(v=List(), x7, y7, t, p); for(x=1, sqrtnint(lim\3, 7), x7=x^7; for(y=x, sqrtnint((lim-x7)\2, 7), y7=y^7; t=x7+y7; forstep(z=y+(x+1)%2, sqrtnint((lim-t)\1, 7), 2, if(isprime(p=t+z^7), listput(v, p))))); Set(v) \\ Charles R Greathouse IV, Feb 27 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 26 2017
STATUS
approved