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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A354951 The number of squarefree abundant numbers whose largest prime divisor is prime(n).

Original entry on oeis.org

0, 0, 1, 3, 5, 13, 27, 59, 125, 257, 534, 1094, 2244, 4607, 9407, 19164, 38939, 79154, 160473, 325213, 658940, 1332598, 2694009, 5440236, 10973874, 22135366, 44644593, 89989907, 181374472, 365371286, 734959945
Offset: 1

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Author

Amiram Eldar, Jun 13 2022

Keywords

Comments

For n >= 3 we have a(n) >= 2^(n-3) as all squarefree numbers whose largest prime divisor are prime(n) that are a multiple of 6*prime(n) are abundant. - David A. Corneth, Jun 13 2022

Examples

			n  prime(n)  a(n)  terms k of A087248 with A006530(k) = prime(n)
-  --------  ----  ---------------------------------------------
1  2         0     -
2  3         0     -
3  5         1     30
4  7         3     42, 70, 210
5  11        5     66, 330, 462, 770, 2310

Crossrefs

Cf. A005117, A006530, A087248, A354950.

Programs

  • Mathematica
    a[n_] := Count[Prime[n] * Divisors[Product[Prime[i], {i, 1, n - 1}]], _?(SquareFreeQ[#] && DivisorSigma[-1, #] > 2 &)]; Array[a, 15]
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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