OFFSET
1,1
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..10000
EXAMPLE
13 is in the sequence because 13^2 - 13 - 1 = 155 = 5 * 31 is semiprime.
18 is in the sequence because 18^2 - 18 - 1 = 305 = 5 * 61 is semiprime.
MAPLE
MATHEMATICA
c = 0; Do[If[PrimeOmega[n^2-n-1] == 2, c++; Print[c, " ", n]], {n, 1, 30000}];
Select[Range[200], PrimeOmega[#^2-#-1]==2&] (* Harvey P. Dale, Sep 21 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Jun 06 2014
STATUS
approved