A186689 Numbers n such that n^4 + 1 is a semiprime.

3, 5, 7, 8, 10, 11, 12, 13, 14, 17, 18, 21, 22, 23, 26, 29, 30, 32, 35, 36, 38, 39, 40, 42, 50, 52, 57, 58, 61, 62, 65, 68, 71, 72, 73, 78, 81, 84, 86, 92, 94, 98, 100, 102, 103, 105, 108, 112, 113, 114, 115, 116, 119, 120, 122, 124, 128, 129, 130, 138, 146, 148, 152, 153, 158

Offset: 1

Author

Michel Lagneau, Feb 25 2011

Keywords

• nonn

Comments

Corresponding semiprimes n^4+1 are in A186688.

Examples

			3 is in the sequence because 3^4 + 1 = 82 = 2*41 is semiprime.
		

Links

• Robert Price, Table of n, a(n) for n = 1..1500

Crossrefs

Cf. A001358, A006313, A085722, A103854, A104238, A104335, A105041, A105066, A105078, A105122, A105142, A105237, A104479, A104494, A104657, A105282, A186688.

Programs

Mathematica

SemiPrimeQ[ n_] := (n > 1) && (2 == Plus @@ (Transpose[FactorInteger[n]][[2]]));
  Select[Range[300], SemiPrimeQ[#^4 + 1] &]
Select[Range[200],PrimeOmega[#^4+1]==2&] (* Harvey P. Dale, Jan 27 2013 *)