A082131 Middle of semiprime triple: n-2, n, n+2 are semiprimes.
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
Keywords
Examples
a(1) = 93 because 91 = 7*13, 93 = 3*31 and 95 = 5*19 are semiprime.
Links
- Harvey P. Dale and David A. Corneth, Table of n, a(n) for n = 1..13739 (terms < 10^6, first 1000 terms from Harvey P. Dale)
Programs
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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 *)
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PARI
isok(n) = (bigomega(n-2) == 2) && (bigomega(n)==2) && (bigomega(n+2) == 2); \\ Michel Marcus, Jul 16 2017
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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
Comments