OFFSET
1,2
COMMENTS
S. W. Golomb, personal communication, Svalbard, Norway, 7/97.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..10000
Harri Hakula, Pauliina Ilmonen, Vesa Kaarnioja, Computation of extremal eigenvalues of high-dimensional lattice-theoretic tensors via tensor-train decompositions, arXiv:1705.05163 [math.NA], 2017. See Table 2, d=4,5.
FORMULA
a(n) = Sum_{k=1..n} A014665(n). - Sean A. Irvine, Nov 15 2018
For n>1: # of positive integers u <= n(n-1) such that p^H_p(u)<=n for all p<=u, where H_p(u) = highest power of p dividing u.
a(n) = A236309(n) + 1. - Andrew Howroyd, Nov 16 2018
MAPLE
A027435 := proc(n)
local L, i, j ;
L := {};
for i from 1 to n do
for j from 1 to n do
if igcd(i, j) = 1 then
L := L union {i*j};
end if;
end do:
end do:
nops(L);
end proc: # R. J. Mathar, Jun 09 2016
MATHEMATICA
Array[-Boole[# > 1] + Length@ Union@ Apply[Join, Table[If[CoprimeQ @@ #, i j, 0] &@ {i, j}, {i, #}, {j, #}]] &, 56] (* Michael De Vlieger, Nov 01 2017 *)
PROG
(PARI) a(n)={#Set(concat(vector(n, i, [i*j | j<-[1..n], gcd(i, j)==1])))} \\ Andrew Howroyd, Nov 15 2018
(PARI) seq(n)={my(v=vector(n), t=1); for(n=1, n, t+=sum(i=1, n-1, gcd(i, n) == 1 && 0==sumdiv(i*n, d, my(t=i*n/d); gcd(t, d)==1 && d<n && t<d)); v[n]=t); v} \\ Andrew Howroyd, Nov 16 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Olivier Gérard, Nov 15 1997
STATUS
approved
