cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A140481 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).

Original entry on oeis.org

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
Offset: 1

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Author

Eric Angelini, Jun 25 2008

Keywords

Examples

			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.

Crossrefs

Cf. A000005, A064491, A140482.

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.

Extensions

More terms from Hans Havermann, Jun 25 2008
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