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A109313
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Difference between prime factors of n-th semiprime.
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5
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0, 1, 0, 3, 5, 2, 4, 9, 0, 11, 8, 15, 2, 17, 10, 21, 0, 14, 6, 16, 27, 29, 8, 20, 35, 4, 39, 12, 41, 26, 6, 28, 45, 14, 51, 34, 18, 57, 10, 0, 59, 38, 40, 12, 65, 44, 69, 2, 24, 71, 26, 77, 50, 16, 81, 0, 56, 87, 58, 32, 6, 95, 64, 99, 22, 36, 101, 8, 68, 105, 38, 24, 107, 70, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| a(n)=0 if sp(n) is a square of prime. Cf. A068318 Sum of prime factors of n-th semiprime.
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LINKS
| Zak Seidov, Table of n, a(n) for n = 1..1000
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EXAMPLE
| a(1)=0 because sp(1)=4=2*2 and 2-2=0; a(2)=1 because sp(2)=6=2*3 and 3-2=1; sp(n)=n-th semiprime.
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MAPLE
| with(numtheory): a:=proc(n) if bigomega(n)=2 and nops(factorset(n))=2 then factorset(n)[2]-factorset(n)[1] elif bigomega(n)=2 then 0 else fi end: seq(a(n), n=1..225); (Emeric Deutsch)
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MATHEMATICA
| semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; f[n_] := Subtract @@ Reverse@ Flatten[ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@ n]; f@# & /@ Select[ Range@ 215, semiPrimeQ]
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CROSSREFS
| Cf. A068318, A178313.
Sequence in context: A084753 A163364 A082822 * A176881 A065188 A065257
Adjacent sequences: A109310 A109311 A109312 * A109314 A109315 A109316
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Jun 27 2005
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