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.

A140335 Smallest number greater than a(n-1) that, when adding the reciprocals of all the terms up to it, the sum is <= 3.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 230, 57960
Offset: 1

Views

Author

J. Lowell, Jul 21 2008

Keywords

Comments

The definition similar to this except that it reaches 2 is simply 1, 2, 3, 6.
The sequence ends at a(13) because Sum_{n=1..13} 1/a(n) = 3. - Joerg Arndt, Sep 06 2019

Examples

			11 does not qualify for the term after 10 because the sum of the reciprocals of the first 11 terms would then fall between 3.01 and 3.02.
		

Crossrefs

Cf. A281873 (sum <= 4).

A306349 Number of terms in the greedy Egyptian fraction representation of n.

Original entry on oeis.org

1, 4, 13, 35, 99
Offset: 1

Views

Author

Pontus von Brömssen, Feb 09 2019

Keywords

Comments

a(n) >= A004080(n).
a(6) > 255 and the denominator of the 255th term in the representation of 6 has 1264021241 digits.

Examples

			a(3)=13 is the number of terms of A140335;
a(4)=35 is the number of terms of A281873.
		

Crossrefs

Programs

  • Python
    from sympy import egyptian_fraction
    def A306349(n): return len(egyptian_fraction((n,1)))

A323725 a(n) is the last (and thus largest) denominator of an Egyptian fraction representing n, where each consecutive denominator is as small as possible.

Original entry on oeis.org

1, 6, 57960, 36802906522516375115639735990520502954652700
Offset: 1

Views

Author

AJ Tatum, Aug 31 2019

Keywords

Comments

Values grow extremely quickly, a(5) has 142548 decimal digits.
The denominators for n = 3 are given in A140335.
The denominators for n = 4 are given in A281873.
The number of terms in the representation of n is A306349(n).

Examples

			a(3) = 57960 because (1/1) + (1/2) + (1/3) + (1/4) + (1/5) + (1/6) + (1/7) + (1/8) + (1/9) + (1/10) + (1/15) + (1/230) + (1/57960) = 3 and the final and greatest denominator is 57960. (Sequence A140335 has the full list of denominators.)
		

Crossrefs

A140335 and A281873 are the denominatorial sequences for 3 and 4, respectively.
Cf. A306349.

Programs

  • PARI
    a(n)={my(s=n,k=1); while(s>1/k, s-=1/k; k++); while(s!=0, k=ceil(1/s); s-=1/k); k} \\ Andrew Howroyd, Sep 01 2019
    
  • Python
    from sympy import egyptian_fraction
    def A323725(n): return egyptian_fraction((n,1))[-1] # Pontus von Brömssen, Aug 03 2020
Showing 1-3 of 3 results.