cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A082131 Middle of semiprime triple: n-2, n, n+2 are semiprimes.

Original entry on oeis.org

93, 121, 143, 185, 203, 215, 217, 219, 289, 301, 303, 321, 393, 413, 415, 471, 517, 535, 581, 669, 687, 697, 791, 815, 1057, 1079, 1135, 1137, 1139, 1147, 1167, 1205, 1255, 1315, 1345, 1347, 1349, 1385, 1387, 1389, 1391, 1403, 1563, 1641, 1687
Offset: 1

Views

Author

Hugo Pfoertner, Apr 04 2003

Keywords

Comments

All terms are odd. - David A. Corneth, Jul 16 2017

Examples

			a(1) = 93 because 91 = 7*13, 93 = 3*31 and 95 = 5*19 are semiprime.
		

Crossrefs

Programs

  • Mathematica
    2#+1&/@Flatten[Position[Partition[If[PrimeOmega[#]==2,1,0]&/@Range[ 1,1701,2],3,1],?(Total[#]==3&),{1},Heads->False]] (* _Harvey P. Dale, Jul 24 2013 *)
  • PARI
    isok(n) = (bigomega(n-2) == 2) && (bigomega(n)==2) && (bigomega(n+2) == 2); \\ Michel Marcus, Jul 16 2017
    
  • PARI
    list(lim)={my(u=primes(primepi(lim\3)), v=List(), t, res = List()); for(i=2, #u, for(j=i, #u, t=u[i]*u[j]; if(t>lim, break); listput(v, t))); listsort(v); for(i=1, #v-2, if(v[i]+4==v[i+2],listput(res,v[i+1]))); res} \\ adapted from Charles R. Greathouse IV at A046315. - David A. Corneth, Jul 16 2017

Extensions

More terms from Jud McCranie, Apr 04 2003