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A074398
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Number of primes between n and phi(n).
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0
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0, 0, 0, 1, 0, 2, 0, 2, 1, 2, 0, 3, 0, 3, 2, 2, 0, 4, 0, 4, 3, 4, 0, 5, 1, 4, 2, 4, 0, 6, 0, 5, 3, 5, 2, 6, 0, 5, 3, 6, 0, 8, 0, 6, 5, 6, 0, 9, 2, 7, 4, 6, 0, 9, 4, 7, 5, 7, 0, 11, 0, 8, 7, 7, 3, 10, 0, 8, 5, 10, 0, 11, 0, 10, 9, 10, 4, 12, 0, 11, 6, 10, 0, 14, 5, 10, 7, 11, 0, 15, 4, 10, 7, 10, 4, 13, 0
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,6
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EXAMPLE
| phi(6) = 2 and there are 2 primes between 2 and 6 (endpoints are excluded), namely 3, 5. 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[n, EulerPhi[n]], {n, 1, 100}]
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CROSSREFS
| Sequence in context: A068067 A046926 A200815 * A144765 A147588 A070824
Adjacent sequences: A074395 A074396 A074397 * A074399 A074400 A074401
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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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