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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

Table of n, a(n) for n=1..5.

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: A305580 A191311 A086714 * A009463 A066260 A248591

Adjacent sequences:  A239320 A239321 A239322 * A239324 A239325 A239326

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 15 2014

STATUS

approved

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Last modified September 27 03:08 EDT 2020. Contains 337380 sequences. (Running on oeis4.)