OFFSET
1,1
COMMENTS
Subsequence of A267088.
Obviously, because of Fermat's Last Theorem, a(n) cannot be a cube.
Corresponding exponents are 2, 5, 2, 8, 2, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 4, 2, ...
Motivation for this sequence is the equation m^k = x^3 + y^3 where m > 0, k >= 2 and x, y are distinct positive integers.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..4707
EXAMPLE
9 is a term because 9 = 3^2 = 1^3 + 2^3.
243 is a term because 243 = 3^5 = 3^3 + 6^3.
576 is a term because 576 = 24^2 = 4^3 + 8^3.
51984 is a term because 51984 = 228^2 = 11^3 + 37^3.
MATHEMATICA
Union@ Select[Plus @@@ Union@ Map[Sort, Permutations[Range[210]^3, {2}]], # == 1 || GCD @@ FactorInteger[#][[All, 2]] > 1 &] (* Michael De Vlieger, Jan 15 2016, after Ant King at A001597 *)
PROG
(PARI) is(n) = for( i=ceil(sqrtn(n\2+1, 3)), sqrtn(n-.5, 3), ispower(n-i^3, 3) & return(1));
for(n=1, 1e7, if(is(n) && ispower(n), print1(n, ", ")));
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Jan 14 2016
STATUS
approved