A092125 Numbers n such that n, n+2, n+4 are semiprimes.

91, 119, 141, 183, 201, 213, 215, 217, 287, 299, 301, 319, 391, 411, 413, 469, 515, 533, 579, 667, 685, 695, 789, 813, 1055, 1077, 1133, 1135, 1137, 1145, 1165, 1203, 1253, 1313, 1343, 1345, 1347, 1383, 1385, 1387, 1389, 1401, 1561, 1639, 1685, 1687, 1761

Offset

1,1

Comments

Semiprimes in arithmetic progression. All terms are odd, see also A056809.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[Table[ #[[2]], {1}] & /@ FactorInteger[n]]; Select[ Range[ 1792], PrimeFactorExponentsAdded[ # ] == PrimeFactorExponentsAdded[ # + 2] == PrimeFactorExponentsAdded[ # + 4] == 2 &] (* Robert G. Wilson v, Feb 24 2004 *)
SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 2000}], {1, _, 1, _, 1}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 17 2020 *)

Prog

(Magma)IsSemiprime:=func< n| &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [2..4300]|IsSemiprime(n) and IsSemiprime(n+2) and IsSemiprime(n+4)] // Vincenzo Librandi, Dec 16 2010

Crossrefs

Cf. A056809, A070552, A092126, A092127, A092128, A092129.

Sequence in context: A140389 A236845 A157345 * A005935 A020307 A351336

Adjacent sequences: A092122 A092123 A092124 * A092126 A092127 A092128

Keyword

easy,nonn

Author

Zak Seidov, Feb 22 2004

Status

approved