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A027435 Number of distinct products ij with 1 <= i <= n, 1 <= j <= n, (i,j)=1. 3
1, 2, 4, 6, 10, 11, 17, 21, 27, 29, 39, 42, 54, 57, 62, 70, 86, 89, 107, 113, 120, 125, 147, 152, 172, 178, 196, 204, 232, 236, 266, 282, 294, 302, 320, 329, 365, 374, 388, 400, 440, 446, 488, 501, 518, 529, 575, 586, 628, 638, 657, 672, 724, 733, 758, 778 (list; graph; refs; listen; history; text; internal format)
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

Cf. A014665, A236309.

Sequence in context: A026429 A086917 A004789 * A014666 A067852 A253968

Adjacent sequences:  A027432 A027433 A027434 * A027436 A027437 A027438

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Olivier Gérard, Nov 15 1997

STATUS

approved

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Last modified March 26 14:18 EDT 2019. Contains 321497 sequences. (Running on oeis4.)