The OEIS is supported by the many generous donors to the OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A239323 Semiprimes of the form (2^n + 1)*(2^n - n + 1). 0
 4, 6, 15, 221, 4294049777 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Generated by n: 0, 1, 2, 4, 16, ... The positions of a(n) in A001358: 1, 2, 6, 75, ... LINKS EXAMPLE 4 is in this sequence because (2^0 + 1)*(2^0 - 0 + 1) = 2*2 = 4 is semiprime for n = 0, 6 is in this sequence because (2^1 + 1)*(2^1 - 1 + 1) = 3*2 = 6 is semiprime for n = 1, 15 is in this sequence because (2^2 + 1)*(2^2 - 2 + 1) = 5*3 = 15 is semiprime for n = 2. PROG (Magma) k := 1;      for n in [1..10000] do         if IsPrime(k*2^n + 1) and IsPrime(k*2^n - n + 1) then            (k*2^n + 1)*(k*2^n - n + 1);         end if;      end for; CROSSREFS Cf. A019434, A100361, A100362. Sequence in context: A191311 A086714 A356801 * A009463 A066260 A248591 Adjacent sequences:  A239320 A239321 A239322 * A239324 A239325 A239326 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Mar 15 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 1 09:13 EDT 2022. Contains 357140 sequences. (Running on oeis4.)