OFFSET
1,3
LINKS
Paul Tek, Table of n, a(n) for n = 1..10000
FORMULA
Ordinal transform of A000005. - Franklin T. Adams-Watters, Aug 28 2006
a(A000040(n)^(p-1)) = n if p is prime. - Robert Israel, May 04 2015
EXAMPLE
a(10)=3 since 6,8,10 each have four divisors. a(11)=5 since 2,3,5,7,11 each have two divisors.
MAPLE
N:= 1000: # to get a(1) to a(N)
R:= Vector(N):
for n from 1 to N do
v:= numtheory:-tau(n);
R[v]:= R[v]+1;
A[n]:= R[v];
od:
seq(A[n], n=1..N); # Robert Israel, May 04 2015
MATHEMATICA
b[_] = 0;
a[n_] := a[n] = With[{t = DivisorSigma[0, n]}, b[t] = b[t]+1];
Array[a, 105] (* Jean-François Alcover, Dec 20 2021 *)
PROG
(PARI) a(n)=my(d=numdiv(n)); sum(k=1, n, numdiv(k)==d) \\ Charles R Greathouse IV, Sep 02 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Henry Bottomley, Dec 21 2001
STATUS
approved