OFFSET
1,2
COMMENTS
FORMULA
a(n) <= 3^(n-1), with equality if n is prime.
a(n) >= A038547(n).
MATHEMATICA
seq[m_] := Module[{p = Select[Range[m], PrimeQ], s = Table[0, {m}], c, nd, ndd}, s[[p]] = 3^(p - 1); c = Length[p]; n = 1; While[c < m, nd = DivisorSigma[0, n]; If[nd <= m && s[[nd]] == 0, ndd = Length@Union[EulerPhi /@ Divisors[n]]; If[ndd == nd, c++; s[[nd]] = n]]; n++]; s]; seq[30]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Oct 06 2021
STATUS
approved