login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Largest of the most frequently occurring numbers in 1-to-n multiplication table.
7

%I #19 Mar 29 2022 08:36:41

%S 1,2,6,4,4,12,12,24,24,40,40,24,24,24,60,60,60,36,36,60,60,60,60,120,

%T 120,120,120,168,168,120,120,120,120,120,120,180,180,180,180,120,120,

%U 120,120,120,360,360,360,360,360,360,360,360,360,360,360,360,360,360

%N Largest of the most frequently occurring numbers in 1-to-n multiplication table.

%H Branden Aldridge, <a href="/A057143/b057143.txt">Table of n, a(n) for n = 1..20000</a> (first 1000 terms from Reinhard Zumkeller).

%e M(n) is the array in which m(x,y)= x*y for x = 1 to n and y = 1 to n. In M(10), the most frequently occurring numbers are 6, 8, 10, 12, 18, 20, 24, 30,40, each occurring 4 times. The largest of these numbers is 40, so a(10) = 40.

%o (Haskell)

%o import Data.List (group, sort, sortBy)

%o import Data.Function (on)

%o a057143 n = head $ head $ reverse $ sortBy (compare `on` length) $

%o group $ sort [u * v | u <- [1..n], v <- [1..n]]

%o -- _Reinhard Zumkeller_, Jun 22 2013

%Y Cf. A057142, A057144, A057338.

%K nonn

%O 1,2

%A _Arran Fernandez_, Aug 13 2000

%E More terms from Larry Reeves (larryr(AT)acm.org), Apr 18 2001