A164000 Main diagonal of array in A163280.

1, 6, 15, 28, 45, 66, 91, 128, 162, 200, 231, 372, 325, 406, 495, 656, 561, 954, 703, 1180, 987, 1078, 1035, 1896, 1375, 1534, 1701, 2324, 1653, 3090, 1891, 3104, 2541, 2686, 3045, 5004, 2701, 3382, 3627, 5560, 3321, 6846, 3655, 6028, 6165, 5014, 4371

Offset: 1

Author

Omar E. Pol, Aug 08 2009

Keywords

• nonn

Crossrefs

Cf. A008578, A161344, A161345, A163280.

Programs

Maple

A033676 := proc(n) local a, d; a := 0 ; for d in numtheory[divisors](n) do if d^2 <= n then a := max(a, d) ; end if; end do: a; end proc: A163280 := proc(n, k) local r, T ; r := 0 ; for T from k^2 by k do if A033676(T) = k then r := r+1 ; if r = n then RETURN(T) ; end if; end if; end do: end proc: A164000 := proc(n) A163280(n,n) ; end proc: seq(A164000(n),n=1..60) ; # R. J. Mathar, Feb 16 2010

Mathematica

nmax = 50;
pm = Prime[nmax];
selDiv[n_] := Select[Divisors[n], #^2 <= n&][[-1]];
Clear[col];
col[k_] := col[k] = Select[Range[k pm], selDiv[#] == k&];
a[n_] := col[n][[n]];
Array[a, nmax] (* Jean-François Alcover, Mar 24 2020 *)

PARI

lista(nn) = my(v = apply(f, [1..(2*nn-1)^2]), cols = vector(nn, i, select(x->(x==i), v, 1))); vector(nn, i, cols[i][i]); \\ Michel Marcus, Jan 23 2023

Extensions

Terms from a(13) on by R. J. Mathar, Feb 16 2010