OFFSET
1,8
COMMENTS
Ordinal transform of A323910.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
MATHEMATICA
f[n_] := 2 n - DivisorSigma[1, n];
Module[{b}, b[_] = 0; a[n_] := With[{t = A323910[n]}, b[t] = b[t] + 1]];
Array[a, 105] (* Jean-François Alcover, Jan 12 2022 *)
PROG
(PARI)
up_to = 65537;
ordinal_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), pt); for(i=1, length(invec), if(mapisdefined(om, invec[i]), pt = mapget(om, invec[i]), pt = 0); outvec[i] = (1+pt); mapput(om, invec[i], (1+pt))); outvec; };
DirInverse(v) = { my(u=vector(#v)); u[1] = (1/v[1]); for(n=2, #v, u[n] = -sumdiv(n, d, if(d<n, v[n/d]*u[d], 0))); (u) }; \\ Compute the Dirichlet inverse of the sequence given in input vector v.
A033879(n) = (2*n-sigma(n));
v331180 = ordinal_transform(DirInverse(vector(up_to, n, A033879(n))));
A331180(n) = v331180[n];
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jan 11 2020
STATUS
approved