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 1-1 of 1 results.

A379753 Numbers that set records in A379752.

Original entry on oeis.org

60, 120, 240, 480, 840, 1260, 1680, 2520, 3360, 5040, 7560, 10080, 15120, 20160, 27720, 36960, 55440, 83160, 110880, 166320, 221760, 277200, 332640, 443520, 498960, 554400, 665280, 720720, 997920, 1081080, 1330560, 1441440, 2162160, 2882880, 3603600, 4324320, 5765760
Offset: 1

Views

Author

Michael De Vlieger, Jan 01 2025

Keywords

Comments

Proper subset of the intersection of A025487 and A375055.
Conjecture: subset of A332785 = A126706 \ A286708.
This sequence seems to be rich in highly composite numbers, the prime shape of a(n) resembles that of highly composite numbers, with long tails of large prime factors with multiplicity 1.
Terms not in A002182 are not all of the form 2^5 * prime(i..j), 1 < i < j, for example, a(24) = 443520 = 2^7 * 3^2 * 5 * 7 * 11.

Examples

			Let b(n) = A379752(n).
Table showing exponents of prime power factors of a(n) for n = 1..12.
Example: a(6) = 1260 = 2^2 * 3^2 * 5 * 7, hence we write "2.2.1.1".
   n      a(n)       Exp.    b(a(n))
  ----------------------------------
   1       60 **   2.1.1        1   6*10
   2      120 **   3.1.1        2   6*20 = 10*12
   3      240 *    4.1.1        3   6*40 = 10*24 = 12*20
   4      480      5.1.1        4   6*80 = 10*48 = 12*40 = 20*24
   5      840 *    3.1.1.1      6   6*140 = 10*84 = 12*70 = 14*60 = 20*42 = 28*30
   6     1260 *    2.2.1.1      7
   7     1680 *    4.1.1.1      9
   8     2520 **   3.2.1.1     11
   9     3360      5.1.1.1     12
  10     5040 **   4.2.1.1     15
  11     7560 *    3.3.1.1     16
  12    10080 *    5.2.1.1     19
*  = a(n) is highly composite (in A002182),
** = a(n) is superior highly composite (in both A002182 and A002201).
		

Crossrefs

Programs

  • Mathematica
    (* Load function f at A025487 *)
    r = 0;
    s = Select[Union@ Flatten@ f[14][[4 ;; -1]], Not@*SquareFreeQ];
    nn = Length[s]; Print[nn];
    Reap[Do[k = s[[i]]; If[# > r, r = #; Sow[k]] &@
      Count[Transpose@ {#, k/#} &@ #[[2 ;; Ceiling[Length[#]/2] ]] &@ Divisors[k],
        _?(And[1 < GCD @@ {##},
           Nor[Divisible[#2, rad[#1]],
               Divisible[#1, rad[#2]] ] ] & @@ # &)], {i, nn}] ][[-1, 1]]
Showing 1-1 of 1 results.