login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A176579 Primes p that exactly one of 2p-1, 2p+1 is semiprime. 1
5, 7, 11, 13, 19, 29, 59, 67, 73, 79, 89, 103, 127, 149, 163, 167, 181, 191, 227, 241, 251, 257, 263, 269, 271, 277, 283, 311, 347, 353, 359, 373, 383, 389, 397, 401, 409, 433, 439, 449, 457, 467, 479, 487, 503, 523, 541, 557, 571, 599, 601, 613, 643, 647, 659, 677, 691, 709, 719, 733, 739, 751, 757, 769, 811, 827, 839, 853 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

a(1)=5 because 2*5-1=9=semiprime and 2*5+1=11=non-semiprime.

MAPLE

Contribution from R. J. Mathar, Dec 12 2010: (Start)

isA001358 := proc(n) is(numtheory[bigomega](n) = 2) ; end proc:

for n from 1 to 120 do p := ithprime(n) ; if isA001358(2*p-1) <> isA001358(2*p+1) then printf("%d, ", p); end if; end do: (End)

MATHEMATICA

Select[Prime[Range[200]], Count[PrimeOmega[2#+{1, -1}], 2]==1&] (* Harvey P. Dale, Oct 05 2015 *)

CROSSREFS

Cf. A001358.

Sequence in context: A088664 A023219 A045438 * A154275 A167460 A045439

Adjacent sequences:  A176576 A176577 A176578 * A176580 A176581 A176582

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Apr 20 2010

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 6 21:48 EST 2019. Contains 329809 sequences. (Running on oeis4.)