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.

Showing 1-3 of 3 results.

A161216 a(n) = A161210(n)*4.

Original entry on oeis.org

0, 4, 12, 28, 56, 84, 112
Offset: 0

Views

Author

Omar E. Pol, Jun 06 2009

Keywords

Links

Crossrefs

Cf. A139250, A152980, A153006, A160160, A161210, A161212, A161214, A161217.

A161219 a(n) = (1/n) * Sum_{d|n} phi(n/d)*2^(d+1).

Original entry on oeis.org

4, 6, 8, 12, 16, 28, 40, 72, 120, 216, 376, 704, 1264, 2364, 4384, 8232, 15424, 29204, 55192, 104976, 199760, 381492, 729448, 1398504, 2684368, 5162856, 9942136, 19175160, 37025584, 71585136, 138547336, 268439592, 520602352, 1010588256, 1963413664, 3817763800
Offset: 1

Views

Author

N. J. A. Sloane, Nov 21 2009

Keywords

Links

Crossrefs

Cf. A000031, A053635, A160619, A161217.

Programs

  • PARI
    a(n) = sumdiv(n, d, eulerphi(n/d)*2^(d+1))/n; \\ Michel Marcus, Apr 15 2021

Formula

G.f.: -2 * Sum_{k>=1} phi(k) * log(1 - 2*x^k) / k. - Ilya Gutkovskiy, Apr 15 2021
a(n) = 2*A000031(n). - Hugo Pfoertner, Jun 24 2021

A161211 First differences of A161210.

Original entry on oeis.org

1, 2, 4, 7, 7, 7
Offset: 1

Views

Author

Omar E. Pol, Jun 06 2009

Keywords

Comments

Number of toothpicks added at the n-th round.

Links

Crossrefs

Cf. A139251, A152980, A160161, A161210, A161213, A161215, A161217.
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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