OFFSET
0,1
FORMULA
a(n) = minimal value of k>0 such that n^5 + k^2 is a semiprime.
EXAMPLE
a(0) = 2 because 0^5 + 1^2 = 1 is not semiprime, but 0^5 + 2^2 = 4 = 2^2 is.
a(1) = 3 because 1^5 + 1^2 and 1^5 + 2^2 are not semiprime, but 1^5 + 3^2 = 10 = 2 * 5 is semiprime.
a(2) = 1 because 2^5 + 1^2 = 33 = 3 * 11 is semiprime.
a(42) = 31 because 42^5 + 31^2 = 130692193 = 571 * 228883 and for no smaller k>0 is 42^4 + k^2 a semiprime.
MATHEMATICA
a[n_] := (For[k = 1, PrimeOmega[n^5 + k^2] != 2, k++]; k); a /@ Range[0, 93] (* Giovanni Resta, Jun 16 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Jun 26 2005
EXTENSIONS
a(46) corrected by Giovanni Resta, Jun 16 2016
STATUS
approved