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A186689
Numbers n such that n^4 + 1 is a semiprime.
1
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
1,1
COMMENTS
Corresponding semiprimes n^4+1 are in A186688.
LINKS
EXAMPLE
3 is in the sequence because 3^4 + 1 = 82 = 2*41 is semiprime.
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 *)
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 25 2011
STATUS
approved