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 1-4 of 4 results.

A122967 Greatest prime factor of the pair of amicable numbers. Amicable numbers are sorted by the smaller number in the pair.

Original entry on oeis.org

71, 37, 131, 251, 199, 79, 139, 1151, 827, 89, 71, 107, 467, 89, 239, 239, 467, 359, 467, 479, 431, 263, 853, 2267, 433, 251, 1439, 2393, 1367, 47, 863, 449, 1217, 701, 4799, 89, 1879, 433, 1063, 2609, 269, 5669, 239, 2099, 6803, 251, 3923, 199, 929, 227, 5119
Offset: 1

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Author

Tanya Khovanova, Oct 27 2006

Keywords

Examples

			220 = 2^2*5*11, 284 = 2^2*71. The greatest prime factor in the pair is 71.

Links

Crossrefs

Cf. A002025, A002046, A006530, A063990 (amicable numbers), A061469 (GCD of the amicable pairs).

Formula

a(n) = max(A006530(A002025(n)), A006530(A002046(n))). - R. J. Mathar, Nov 10 2006

Extensions

More terms from R. J. Mathar, Nov 10 2006

A180326 The non-common part of the smaller number of an amicable pair.

Original entry on oeis.org

55, 592, 655, 1255, 779, 1343, 117, 1081, 685, 4183, 497, 85, 7975, 2233, 209, 7648, 17708, 14231, 10741, 11017, 23171, 4471, 70135, 77155, 22825, 44551, 27341, 4786, 31441, 893, 75049, 76241, 78023, 79453, 80417, 166991, 90763, 7645, 54982, 112277
Offset: 1

Views

Author

T. D. Noe, Sep 07 2010

Keywords

Comments

All terms are composite numbers. Very few duplicates occur: for the amicable numbers less than 10^14, a number appears at most twice.

Links

Crossrefs

Cf. A180327 (non-common part of the larger number of an amicable pair)

Formula

a(n) = A002025(n) / gcd(A002025(n),A002046(n)) = A002025(n) / A061469(n).

A180327 The non-common part of the larger number of an amicable pair.

Original entry on oeis.org

71, 605, 731, 1391, 796, 1357, 139, 1151, 827, 4187, 527, 107, 8873, 2759, 239, 7697, 19147, 16873, 11021, 11303, 25429, 4601, 91271, 97481, 30743, 49949, 28459, 4961, 32171, 899, 83711, 85759, 86407, 89027, 81583, 195889, 99587, 8227, 56339, 122623
Offset: 1

Views

Author

T. D. Noe, Sep 07 2010

Keywords

Comments

Very few duplicates occur: for the amicable numbers less than 10^14, a number appears at most twice.

Links

Crossrefs

Cf. A180326 (non-common part of the smaller number of an amicable pair)

Formula

a(n) = A002046(n) / gcd(A002025(n),A002046(n)) = A002046(n) / A061469(n).

A297850 Least common prime factor of the members of n-th amicable pair, or 0 if the two members of the pair are coprime.

Original entry on oeis.org

2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 2, 3, 2, 3, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 2, 2
Offset: 1

Views

Author

Felix Fröhlich, Jan 10 2018

Keywords

Comments

The question whether a(n) = 0 for any n is an open problem.
This is different from A171092 (cf. Chernykh link).
If a(n) = 0, then A001221(A259180(2*n-1)*A259180(2*n)) > 21 (cf. Hagis, 1975).

Links

Crossrefs

Cf. A002025, A020639, A061469, A122967, A171092, A259180, A297934.

Formula

a(n) = A297934(A259180(2*n), A259180(2*n-1)).
a(n) = A020639(A061469(n)), if A061469(n) > 1 and 0 otherwise. - Amiram Eldar, Dec 13 2020

Extensions

Offset corrected and more terms added by Amiram Eldar, Dec 13 2020
Showing 1-4 of 4 results.

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

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