A176579 Primes p that exactly one of 2p-1, 2p+1 is semiprime.

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

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: A023219 A343448 A045438 * A154275 A339347 A167460

Adjacent sequences: A176576 A176577 A176578 * A176580 A176581 A176582

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 20 2010

Status

approved