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.

A064041 Number of divisors of A064040(n).

Original entry on oeis.org

4, 4, 6, 4, 4, 6, 6, 4, 4, 8, 4, 6, 8, 4, 4, 4, 9, 4, 4, 8, 8, 6, 6, 4, 10, 6, 4, 6, 8, 4, 8, 4, 4, 12, 4, 6, 4, 8, 6, 4, 8, 12, 4, 6, 6, 4, 8, 10, 4, 12, 4, 4, 4, 8, 12, 4, 6, 4, 4, 4, 12, 6, 6, 9, 8, 8, 8, 4, 12, 8, 4, 10, 8, 4, 6, 6, 4, 4, 16, 4, 4, 6, 12, 4, 8, 12, 4, 4, 8, 8, 8, 12, 4, 4, 4, 15, 4
Offset: 1

Views

Author

Lior Manor, Aug 23 2001

Keywords

Examples

			a(17) = 9 since 36 is the 17th number with prime number of prime divisors and 36 is divisible by 9 numbers.

Links

Crossrefs

Cf. A064040.

Programs

  • PARI
    { n=0; for (m=1, 10^9, if (isprime(omega(m)), write("b064041.txt", n++, " ", numdiv(m)); if (n==1000, break)) ) } \\ Harry J. Smith, Sep 06 2009

A168638 Number of distinct prime divisors of n is 2 or 3.

Original entry on oeis.org

6, 10, 12, 14, 15, 18, 20, 21, 22, 24, 26, 28, 30, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105, 106
Offset: 1

Views

Author

Juri-Stepan Gerasimov, Dec 01 2009

Keywords

Examples

			2310=2*3*5*7*11 has 5 prime factors, hence it is not here, but it is part of A064040.

Links

Programs

Formula

a(n) ~ A033992(n) ~ 2n log n / (log log n)^2. - Charles R Greathouse IV, Jul 28 2016

A105642 Composite nonsquares and noncubes.

Original entry on oeis.org

6, 10, 12, 14, 15, 18, 20, 21, 22, 24, 26, 28, 30, 32, 33, 34, 35, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 102, 104, 105, 106, 108
Offset: 1

Views

Author

Zak Seidov, May 03 2005

Keywords

Crossrefs

Cf. A007774, A024619, A030231, A056760, A064040, A084227, A100658.

Programs

  • Mathematica
    nn=200; Complement[Range[nn], Prime[Range[PrimePi[nn]]], Range[Sqrt[nn]]^2, Range[nn^(1/3)]^3]  (* Harvey P. Dale, Jan 26 2011 *)
  • PARI
    is(n)=n>1 && !isprime(n) && !issquare(n) && !ispower(n,3) \\ Charles R Greathouse IV, Oct 19 2015

Formula

a(n) = n + O(n/log n). - Charles R Greathouse IV, Oct 19 2015
Showing 1-3 of 3 results.

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

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