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A185008
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Next semiprime after 10*n.
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3
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4, 14, 21, 33, 46, 51, 62, 74, 82, 91, 106, 111, 121, 133, 141, 155, 161, 177, 183, 194, 201, 213, 221, 235, 247, 253, 262, 274, 287, 291, 301, 314, 321, 334, 341, 355, 361, 371, 381, 391, 403, 411, 422, 437, 445, 451, 466, 471, 481, 493, 501, 511, 526, 533
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OFFSET
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0,1
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COMMENTS
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LINKS
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FORMULA
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a(n) = MIN[k in A218255 and k > 10*n].
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EXAMPLE
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a(0) = 4 because 4=2^2 is the least semiprime > 10*0=0.
a(1) = 14 because 14=2*7 is the least semiprime > 10*1=10.
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MATHEMATICA
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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]; Table[NextSemiprime[10*n], {n, 0, 100}] (* T. D. Noe, Nov 02 2012 *)
nsp[n_]:=Module[{k=n+1}, While[PrimeOmega[k]!=2, k++]; k]; Table[nsp[10n], {n, 0, 60}] (* Harvey P. Dale, Mar 17 2023 *)
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PROG
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(Python)
from sympy.ntheory.factor_ import primeomega
def nextsemiprime(n):
while primeomega(n + 1) != 2: n += 1
return n + 1
def a(n): return nextsemiprime(10*n)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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