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the wiki complement to the On-Line Encyclopedia of Integer Sequences.
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  • A239797 Decimal expansion of .
  • A238271 Decimal expansion of .
  • A237042 UPC check digits.
  • A236603 Lowest canonical Gray cycles of length .
  • A235365 Smallest odd prime factor of .
  • A234522 Decimal expansion of .
  • A233748 Number of graphs on n vertices with edges colored with at most four interchangeable colors under the symmetries of the full edge permutation group.
  • A232499 Number of unit squares, aligned with a Cartesian grid, completely within the first quadrant of a circle centered at the origin ordered by increasing radius.
  • A231963 Concatenate with its UPC check digit.
  • A230624 Numbers with property that for every base , there is a number such that , where is the sum of digits in the base expansion of .


Sequence of the Day

Sequence of the Day for September 23

A005231: Odd abundant numbers.

{ 945, 1575, 2205, 2835, 3465, 4095, 4725, ... }

Yes, the very first abundant number to be odd is 945, the 232nd abundant number! The first abundant number is even, namely, 12.


No, the odd abundant numbers are not all divisible by 3 or 5, e.g.

  • The first odd abundant number not divisible by 5 is 81081, this being the 175th odd abundant number (and the ?th abundant number).
  • The first odd abundant number not divisible by 3 is 5391411025, this being the ?th odd abundant number (and the ?th abundant number).
  • The first odd abundant number not divisible by neither 3 nor 5 is 20169691981106018776756331, this being the ?th odd abundant number (and the ?th abundant number).

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On this day...

Template:Today in Math History for September 23

Sequences in the news

Sequences in the News

  • Feb 01 2018 Alphabet announced a $8,589,869,056 = $A000396(6) stock buyback.
  • Jan 03 2018 Largest known term of A000043 announced: 77232917.
  • Nov 18 2016 PrimeGrid proves that 10223 is not a Sierpinski number, since 10223 × 2 31172165 + 1 is prime. So no changes to A076336 for now.
  • Sep 14 2016 Tom Greer discovers the twin primes 2996863034895 × 2 1290000 ± 1 using PrimeGrid, TwinGen and LLR.
  • Jan 19 2016 Largest known term of A000043 announced: 74207281, also discovered by Curtis Cooper.
  • Mar 02 2014 Fredrik Johansson announces a computation of the partition number p(10 20) ≈ 1.8381765 × 10 11140086259, the largest known term of A000041.
  • Dec 06 2013 Microsoft launches a challenge to find large non-Mersenne primes, A138837.


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