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A082131 Middle of semiprime triple: n-2, n, n+2 are semiprimes. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

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)

EXAMPLE

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

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 *)

PROG

(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

CROSSREFS

Cf. A001358, A046315, A082130.

Sequence in context: A039550 A167776 A099019 * A249300 A153684 A048257

Adjacent sequences:  A082128 A082129 A082130 * A082132 A082133 A082134

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Apr 04 2003

EXTENSIONS

More terms from Jud McCranie, Apr 04 2003

STATUS

approved

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Last modified October 23 21:57 EDT 2019. Contains 328373 sequences. (Running on oeis4.)