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A099774
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Number of divisors of 2*n-1.
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8
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1, 2, 2, 2, 3, 2, 2, 4, 2, 2, 4, 2, 3, 4, 2, 2, 4, 4, 2, 4, 2, 2, 6, 2, 3, 4, 2, 4, 4, 2, 2, 6, 4, 2, 4, 2, 2, 6, 4, 2, 5, 2, 4, 4, 2, 4, 4, 4, 2, 6, 2, 2, 8, 2, 2, 4, 2, 4, 6, 4, 3, 4, 4, 2, 4, 2, 4, 8, 2, 2, 4, 4, 4, 6, 2, 2, 6, 4, 2, 4, 4, 2, 8, 2, 3, 6, 2, 6, 4, 2, 2, 4, 4, 4, 8, 2, 2, 8, 2, 2, 4, 4, 4, 6, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| G.f.: Sum_{k>0} x^k/(1-x^(2*k-1)) . - Michael Somos Sep 02 2006
G.f.: sum(k=1, infinity, x^((2*k-1)^2/2+1/2) * (1+x^(2*k-1))/(1-x^(2*k-1)) ) [From Joerg Arndt, Nov 08 2010]
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EXAMPLE
| a(5)=3 because the divisors of 9 are: 1, 3 and 9.
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MAPLE
| with(numtheory): seq(tau(2*n-1), n=1..120);
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PROG
| (PARI) {a(n)=if(n<1, 0, numdiv(2*n-1))} /* Michael Somos Sep 03 2006 */
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CROSSREFS
| Bisection of A000005.
Cf. A000005, A099777.
Sequence in context: A104011 A176775 A175778 * A142240 A048288 A050677
Adjacent sequences: A099771 A099772 A099773 * A099775 A099776 A099777
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Nov 19 2004
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 03 2004
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