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 A131109 a(n) is the smallest semiprime such that difference between a(n) and next semiprime, b(n), is n. 12
 9, 4, 6, 10, 69, 15, 26, 169, 146, 237, 95, 1082, 818, 597, 1603, 2705, 2078, 4511, 1418, 2681, 14545, 13863, 37551, 6559, 16053, 55805, 26707, 17965, 308918, 32777, 41222, 35103, 393565, 219509, 153263, 87627, 2263057, 35981, 1789339, 741841, 797542 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This is the semiprime analogous to A000230. - Robert G. Wilson v, Jun 13 2013 LINKS T. D. Noe and Klaus Brockhaus, Table of n, a(n) for n=1..100 FORMULA a(n) = A001358(A123375(n)) - T. D. Noe, Sep 28 2007 EXAMPLE n, b(n)-a(n): 1=10-9, 2=6-4, 3=9-6, 4=14-10, 5=74-69, 6=21-15, 7=33-26, 8=177-169, 9=155-146, 10=247-237, 11=106-95, 12=1094-1082, 13=831-818, 14=611-597, 15=1618-1603, 16=2721-2705, 17=2095-2078, 18=4529-4511, 19=1437-1418, 20=2701-2681, 21=14566-14545, 22=13885-13863, 23=37574-37551, 24=6583-6559, 25=16078-16053, 26=55831-55805, 27=26734-26707, 28=17993-17965, 29=308947-308918, 30=32807-32777, 31=41253-41222, 32=35135-35103, 33=393598-393565, 34=219543-219509, 35=153298-153263, 36=87663-87627, 37=2263094-2263057, 38=36019-35981. MATHEMATICA SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; NextSemiPrime[n_] := Module[{m = n + 1}, While[! SemiPrimeQ[m], m++]; m]; nn = 30; t = Table[0, {nn}]; found = 0; sp0 = 4; While[found < nn, sp1 = NextSemiPrime[sp0]; d = sp1 - sp0; If[d <= nn && t[[d]] == 0, t[[d]] = sp0; found++]; sp0 = sp1]; t (* T. D. Noe, Oct 02 2012 *) CROSSREFS Cf. A065516, A133478. Sequence in context: A088539 A245084 A199054 * A267315 A247412 A154397 Adjacent sequences:  A131106 A131107 A131108 * A131110 A131111 A131112 KEYWORD nonn AUTHOR Zak Seidov, Sep 24 2007 EXTENSIONS Corrected and extended by T. D. Noe and R. J. Mathar, Sep 28 2007 STATUS approved

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Last modified August 24 03:20 EDT 2019. Contains 326260 sequences. (Running on oeis4.)