This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A086005 Semiprimes sandwiched between semiprimes. 12
 34, 86, 94, 122, 142, 202, 214, 218, 302, 394, 446, 634, 698, 842, 922, 1042, 1138, 1262, 1346, 1402, 1642, 1762, 1838, 1894, 1942, 1982, 2102, 2182, 2218, 2306, 2362, 2434, 2462, 2518, 2642, 2722, 2734, 3098, 3386, 3602, 3694, 3866, 3902 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS These are some of the balanced semiprimes (see A213025). - Alonso del Arte, Jun 04 2012 LINKS T. D. Noe, Table of n, a(n) for n=1..10000 Eric Weisstein's World of Mathematics, Semiprime FORMULA a(n) = 2*A086006(n). a(n) = A056809(n)+1. - Zak Seidov, Sep 30 2012 EXAMPLE 94 = 47*2: 94 - 1 = 3*31 and 94 + 1 = 5*19, therefore 94 is in the sequence. MATHEMATICA u[n_]:=Plus@@Last/@FactorInteger[n]==2; lst={}; Do[If[u[n], sp=n; If[u[sp-1]&&u[sp+1], AppendTo[lst, sp]]], {n, 8!}]; lst  (* Vladimir Joseph Stephan Orlovsky, Nov 16 2009 *) (* First run program for A109611 to define semiPrimeQ *) Select[Range[4000], Union[{semiPrimeQ[# - 1], semiPrimeQ[#], semiPrimeQ[# + 1]}] == {True} &] (* Alonso del Arte, Jun 03 2012 *) Select[Partition[Range@ 4000, 3, 1], Union@ PrimeOmega@ # == {2} &][[All, 2]] (* Michael De Vlieger, Jun 14 2017 *) PROG (Haskell) a086005 n = a086005_list !! (n-1) a086005_list = filter    (\x -> a064911 (x - 1) == 1 && a064911 (x + 1) == 1) a100484_list -- Reinhard Zumkeller, Aug 08 2013, Jun 10 2012 CROSSREFS Cf. A001358, A056809. Cf. A064911, A100484. Sequence in context: A260276 A278311 A213025 * A169834 A248201 A140602 Adjacent sequences:  A086002 A086003 A086004 * A086006 A086007 A086008 KEYWORD nonn AUTHOR Reinhard Zumkeller, Jul 07 2003 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 17 03:07 EDT 2019. Contains 325092 sequences. (Running on oeis4.)