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A140481
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a(1) = 1; for n >= 1, a(n+1) is obtained by adding to a(n) the a(n)-th smallest number not dividing a(n).
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1
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1, 3, 8, 20, 46, 96, 204, 420, 864, 1752, 3520, 7068, 14160, 28360, 56736, 113508, 227040, 454176, 908424, 1816944, 3633908, 7267828, 14535662, 29071328, 58142704, 116285418, 232570884, 465141864, 930283760, 1860567600
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| a(n+1) = 2*a(n) + tau(a(n)) (cf. A000005). - Hans Havermann and Franklin T. Adams-Watters, Jun 25 2008. Using a(n+1) = a(n) + tau(a(n)) would give A064491.
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EXAMPLE
| The smallest number not dividing 1 is 2, so a(2) = 1+2 = 3.
The numbers not dividing 3 are 2, 4, 5, 6, ..., so a(3) = 3+5 = 8.
The numbers not dividing 8 are 3, 5, 6, 7, 9, 10, 11, 12, ..., so a(4) = 8+12 = 20.
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CROSSREFS
| Cf. A000005, A064491, A140482.
Sequence in context: A014628 A034504 A191522 * A027928 A026624 A026690
Adjacent sequences: A140478 A140479 A140480 * A140482 A140483 A140484
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KEYWORD
| nonn
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AUTHOR
| Eric Angelini (Eric.Angelini(AT)kntv.be), Jun 25 2008
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EXTENSIONS
| More terms from Hans Havermann (gladhobo(AT)teksavvy.com), Jun 25 2008
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