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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A180202 The product of the two numbers in an amicable pair, A002025(n) * A002046(n).

Original entry on oeis.org

62480, 1432640, 7660880, 27931280, 39685376, 116636864, 179299575, 318523136, 4794813680, 4483640576, 4773473775, 6100571295, 7076217500, 12475715175, 17094480975, 15069863936, 21699524864, 24011966300, 30304399616
Offset: 1

Views

Author

T. D. Noe, Aug 15 2010

Keywords

Comments

This sequence initially shares many terms with A180163 because small amicable pairs are sometimes consecutive terms in the sorted list of amicable numbers, A063990.
First differs from A180163 at a(9). - Omar E. Pol, Oct 25 2017

Examples

			a(9) = A002025(9) * A002046(9) = 63020 * 76084 = 4794813680.

Links

Crossrefs

Cf. A002025, A002046, A180163, A259180.

Programs

  • Mathematica
    s[n_] := DivisorSigma[1,n]-n; smallAmicableQ[n_] := Module[{b=s[n]}, n

Formula

a(n) = A259180(2n-1) * A259180(2n). - Omar E. Pol, Oct 22 2017

A180277 a(n) = A002952(n) + A002953(n).

Original entry on oeis.org

240, 2400, 40320, 72576, 94080, 120960, 141120, 311040, 403200, 483840, 483840, 725760, 673920, 1010880, 1209600, 1497600, 1411200, 1612800, 1747200, 2246400, 2177280, 2371200, 2449440, 2419200, 2620800, 2903040, 3144960, 3110400
Offset: 1

Views

Author

Jonathan Vos Post, Aug 23 2010

Keywords

Examples

			a(1) = 114 + 126 = 240 = 2^4 * 3 * 5.
a(2) = 1140 + 1260 = 2400 = 2^5 * 3 * 5^2.
a(10) = a(11) - why?

Links

Crossrefs

Cf. A002952, A002953, A161005, A180163.

Formula

a(n) = A002952(n) + A002953(n).
{(j+k) such that sigma*(j) = sigma*(k) = j+k, where sigma*(n) is the unitary divisor function A034448}.

Extensions

Extended by R. J. Mathar, Aug 26 2010
Shorter name using given formula from Joerg Arndt, Jul 29 2024
Showing 1-2 of 2 results.

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