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A131109
a(n) is the smallest semiprime such that difference between a(n) and next semiprime, b(n), is n.
14
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
OFFSET
1,1
COMMENTS
This is the semiprime analogous to A000230. - Robert G. Wilson v, Jun 13 2013
LINKS
Martin Raab, Table of n, a(n) for n = 1..120, terms up to a(100) from T. D. Noe and Klaus Brockhaus
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
Sequence in context: A088539 A245084 A199054 * A371881 A267315 A247412
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