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!)
A217195 Primes p such that p-2 is the greatest semiprime less than p. 2
17, 37, 41, 53, 67, 71, 79, 89, 97, 113, 131, 157, 163, 211, 223, 239, 251, 269, 293, 307, 311, 331, 337, 367, 373, 379, 397, 409, 419, 439, 449, 487, 491, 499, 521, 547, 593, 599, 613, 631, 673, 683, 691, 701, 709, 733, 739, 751, 757, 769, 773, 787, 809 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is a subsequence of A063638.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

EXAMPLE

487 is prime, 486 = 2*3^5 is not semiprime and 485 = 5*97 is semiprime.

MATHEMATICA

SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Prime[Range[200]], ! SemiPrimeQ[# - 1] && SemiPrimeQ[# - 2] &] (* T. D. Noe, Sep 27 2012 *)

PROG

(PARI) forprime(p=3, 9999, bigomega(p-2)==2 && bigomega(p-1)!=2 & print1(p", "))

CROSSREFS

Sequence in context: A190755 A098849 A319059 * A177835 A075698 A165493

Adjacent sequences:  A217192 A217193 A217194 * A217196 A217197 A217198

KEYWORD

nonn

AUTHOR

Antonio Roldán, Sep 27 2012

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 14 07:03 EST 2019. Contains 329978 sequences. (Running on oeis4.)