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A092207 Semiprimes k such that k+2 is also a semiprime. 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 October 19 20:37 EDT 2021. Contains 348091 sequences. (Running on oeis4.)