A082663 Odd semiprimes pq with p < q < 2p.

15, 35, 77, 91, 143, 187, 209, 221, 247, 299, 323, 391, 437, 493, 527, 551, 589, 667, 703, 713, 851, 899, 943, 989, 1073, 1147, 1189, 1247, 1271, 1333, 1363, 1457, 1517, 1537, 1591, 1643, 1739, 1763, 1829, 1891, 1927, 1961, 2021, 2173, 2183, 2257, 2279

Offset: 1

Author

Naohiro Nomoto, May 18 2003

Keywords

• easy
• nonn

Comments

Numbers k such that A082647(k) = A000005(k) - 1 = 3.

A082647(p^2) = A000005(p^2) - 1 = 2, where p is odd prime.

Numbers n such that A229964(n) = 2. - Eric M. Schmidt, Oct 05 2013

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1...1000 from Vincenzo Librandi)

Crossrefs

Cf. A000005, A056913, A046388, A082647, A229964.

Programs

Mathematica

f[n_]:=Last/@FactorInteger[n]=={1,1}&&FactorInteger[n][[1,1]]>2&&Floor[FactorInteger[n][[2,1]]/FactorInteger[n][[1,1]]]==1;lst={};Do[If[f[n],AppendTo[lst,n]],{n,7!}];lst (* Vladimir Joseph Stephan Orlovsky, May 19 2010 *)
pq2pQ[n_]:=Module[{fi=FactorInteger[n][[All,1]]},PrimeOmega[n]==2 && fi[[1]]< fi[[2]]< 2fi[[1]]]; Select[Range[1,2301,2],pq2pQ]//Quiet (* Harvey P. Dale, Jul 31 2021 *)

PARI

list(lim)=my(v=List()); forprime(p=3, sqrtint(lim\=1), forprime(q=p+1,min(lim\p,2*p), listput(v,p*q))); Set(v) \\ Charles R Greathouse IV, Mar 03 2021

Extensions

New name based on a Jan 23 2004 comment from Vladeta Jovovic - Charles R Greathouse IV, Mar 03 2021