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A092207 Numbers n such that n and n+2 are semiprimes. 13
4, 33, 49, 55, 85, 91, 93, 119, 121, 141, 143, 159, 183, 185, 201, 203, 213, 215, 217, 219, 235, 247, 265, 287, 289, 299, 301, 303, 319, 321, 327, 339, 391, 393, 411, 413, 415, 445, 451, 469, 471, 515, 517, 527, 533, 535, 543, 551, 579, 581, 589, 633, 667 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Starting with 33 all terms are odd. First squares are 4, 49, 169, 361, 529, 961, 1369, 2209, 2809, 4489,... - Zak Seidov, Feb 17 2017

LINKS

Zak Seidov, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Semiprime

MATHEMATICA

PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[Table[ #[[2]], {1}] & /@ FactorInteger[n]]; Select[ Range[ 668], PrimeFactorExponentsAdded[ # ] == PrimeFactorExponentsAdded[ # + 2] == 2 &]

Select[Range[700], PrimeOmega[#]==PrimeOmega[#+2]==2&] (* Harvey P. Dale, Aug 20 2011 *)

SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 700}], {1, _, 1}] [[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 29 2017 *)

PROG

(PARI) is(n)=if(n%2==0, return(n==4)); bigomega(n)==2 && bigomega(n+2)==2 \\ Charles R Greathouse IV, Feb 21 2017

CROSSREFS

Cf. A056809, A070552, A092125, A092126, A092127, A092128, A092129, A082919, A092209.

Sequence in context: A059904 A145645 A042831 * A133630 A279866 A066645

Adjacent sequences:  A092204 A092205 A092206 * A092208 A092209 A092210

KEYWORD

nonn

AUTHOR

Robert G. Wilson v and Zak Seidov, Feb 24 2004

STATUS

approved

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Last modified June 25 03:03 EDT 2017. Contains 288708 sequences.