1,4

Robert Israel, Table of n, a(n) for n = 1..10000

a(n) = card( k : sigma(k) < n ); a(n) is asymptotic to c*n with c=0.67...

N:= 100: # to get a(1)..a(N)

V:= Vector(N):

for n from 1 to N-2 do

s:= numtheory:-sigma(n)+1;

if s <= N then V[s]:= V[s]+1 fi;

od:

ListTools:-PartialSums(V); # Robert Israel, Jan 08 2018

(PARI) a(n)=sum(i=1, n, if(1+sign(sigma(i)-n), 0, 1))

Partial sums of A054973.

Cf. A000203.

Sequence in context: A157222 A064047 A111899 * A013928 A172104 A006161

Adjacent sequences: A074750 A074751 A074752 * A074754 A074755 A074756

nonn

Benoit Cloitre, Sep 28 2002

approved