OFFSET
1,1
EXAMPLE
21 = 3 * 7 = 2^4 + 4 + 1
MATHEMATICA
f[n_]:=Last/@FactorInteger[n]=={1, 1}; Select[Array[2^#+#+1&, 140, 0], f[ # ]&]
Select[Table[2^k+k+1, {k, 0, 200}], PrimeNu[#]==PrimeOmega[#]==2&] (* Harvey P. Dale, Jul 11 2023 *)
PROG
(PARI) is(n) = my(f = factor(n), e = logint(n, 2)); f[, 2] == [1, 1]~ && n == 1<<e + e + 1 \\ David A. Corneth, May 27 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Apr 07 2010
EXTENSIONS
Name corrected by David A. Corneth, May 27 2023
STATUS
approved