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A074397
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Number of primes between sigma(n) and n.
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0
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0, 0, 0, 1, 0, 2, 0, 2, 1, 3, 0, 4, 0, 3, 3, 4, 0, 5, 0, 5, 3, 3, 0, 8, 1, 4, 3, 7, 0, 10, 0, 7, 4, 5, 4, 13, 0, 5, 4, 12, 0, 11, 0, 9, 7, 6, 0, 15, 1, 9, 5, 10, 0, 14, 4, 14, 6, 8, 0, 22, 0, 6, 9, 12, 5, 16, 0, 11, 5, 15, 0, 24, 0, 9, 9, 13, 3, 18, 0, 20, 8, 8, 0, 25, 5, 9, 7, 18, 0, 27, 5, 15, 7
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,6
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EXAMPLE
| sigma(6) = 12 and there are 2 primes between 6 and 12 (endpoints are excluded), namely 7, 11. Hence a(6) = 2.
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MATHEMATICA
| (*gives number of primes < n*) f[n_] := Module[{r, i}, r = 0; i = 1; While[Prime[i] < n, i++ ]; i - 1]; (*gives number of primes between m and n with endpoints excluded*) g[m_, n_] := Module[{r}, r = f[m] - f[n]; If[PrimeQ[n], r = r - 1]; r]; Table[g[DivisorSigma[1, n], n], {n, 1, 100}]
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CROSSREFS
| Sequence in context: A159780 A138036 A055136 * A082023 A078152 A191247
Adjacent sequences: A074394 A074395 A074396 * A074398 A074399 A074400
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Sep 24 2002
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