The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A062857 Size of smallest square multiplication table which contains some number at least n times. 6
 1, 2, 4, 6, 12, 12, 18, 20, 30, 30, 40, 40, 60, 60, 72, 72, 90, 90, 120, 120, 140, 140, 168, 168, 180, 180, 210, 210, 252, 252, 280, 280, 315, 315, 336, 336, 360, 360, 420, 420, 504, 504, 560, 560, 630, 630, 672, 672, 720, 720, 792, 792, 840, 840, 924, 924, 990 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is the least number m such that there exists k with 1 <= k <= m^2 such that k has at least n divisors t with k/m <= t <= m. - Robert Israel, Jan 30 2017 LINKS EXAMPLE a(7)=18 because the 18 X 18 multiplication table is the smallest to contain a product of frequency 7 (namely the number A062856(7)=36). MATHEMATICA a = 1; a[n_] := a[n] = For[m = a[n-1], True, m++, T = Table[i j, {i, m}, {j, m}] // Flatten // Tally; sel = SelectFirst[T, #[] >= n&]; If[sel != {}, Print[n, " ", m, " ", sel[]]; Return[m]]]; Table[a[n], {n, 1, 60}] (* Jean-François Alcover, Mar 25 2019 *) PROG (MATLAB) N = 1000; % to get all terms with a(n) <= N M = sparse(1, N^2); A(1) = 1; imax = 1; for k = 2:N   M(k*[1:k-1]) = M(k*[1:k-1])+2;   M(k^2) = 1;   newimax = max(M);   A(imax+1:newimax) = k;   imax = newimax; end A  % Robert Israel, Jan 30 2017 CROSSREFS The least such number is A062856(n). Cf. A027424, A062851, A062854, A062855, A062856, A062858, A062859. Sequence in context: A332824 A053146 A056675 * A061799 A076868 A056793 Adjacent sequences:  A062854 A062855 A062856 * A062858 A062859 A062860 KEYWORD nonn AUTHOR Ron Lalonde (ronronronlalonde(AT)hotmail.com), Jun 25 2001 EXTENSIONS More terms from Don Reble, Nov 08 2001 Name clarified by Robert Israel, Jan 30 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 10 19:52 EDT 2020. Contains 336381 sequences. (Running on oeis4.)