A049642 Number of divisors of n does not divide sum of divisors of n.

2, 4, 8, 9, 10, 12, 16, 18, 24, 25, 26, 28, 32, 34, 36, 40, 48, 50, 52, 58, 63, 64, 72, 74, 75, 76, 80, 81, 82, 84, 88, 90, 98, 100, 104, 106, 108, 112, 117, 120, 121, 122, 124, 128, 130, 136, 144, 146, 148, 152, 156, 160, 162, 170, 171, 172, 175

Offset

1,1

Comments

A054025(a(n)) > 0. - Reinhard Zumkeller, Jan 06 2012

A245656(a(n)) = 0. - Reinhard Zumkeller, Jul 28 2014

References

Handbook of Number Theory, D. S. Mitrinovic et al., Kluwer, Section III.51.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Wikipedia, Arithmetic number

Maple

isA049642 := proc(n)
    if modp(numtheory[sigma](n), numtheory[tau](n)) = 0 then
        false;
    else
        true;
    end if;
end proc:
A049642 := proc(n)
    option remember;
    if n = 1 then
        2;
    else
        for a from procname(n-1)+1 do
            if isA049642(a) then
                return a;
            end if;
        end do:
    end if;
end proc: # R. J. Mathar, Oct 26 2015

Mathematica

Select[Range[175], Mod[DivisorSigma[1, #], DivisorSigma[0, #]] > 0 &] (* Jayanta Basu, Mar 28 2013 *)

Prog

(Haskell)
a049642 n = a049642_list !! (n-1)
a049642_list = filter ((== 0) . a245656) [1..]
-- Reinhard Zumkeller, Jan 06 2012
(GAP) a:=Filtered([1..180], n->Sigma(n) mod Tau(n)>0);; Print(a); # Muniru A Asiru, Jan 25 2019

Crossrefs

Complement of A003601.

Cf. A000005, A000203.

Cf. A245656.

Sequence in context: A047466 A003485 A072602 * A326713 A328945 A050907

Adjacent sequences: A049639 A049640 A049641 * A049643 A049644 A049645

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved