cp's OEIS Frontend

A373532 a(n) is the least number k such that A373531(k) = n, or -1 if no such k exists.

%I A373532 #12 Jun 10 2024 15:00:22
%S A373532 1,2,12,120,240,3276,2520,10920,21840,32760,65520,622440,600600,
%T A373532 900900,3636360,1801800,3603600,4455360,22407840,8910720,17821440,
%U A373532 51351300,46060560,69090840,92121120,126977760,138181680,380933280,245044800,414545040,490089600,507911040
%N A373532 a(n) is the least number k such that A373531(k) = n, or -1 if no such k exists.
%F A373532 a(n) >= A061799(n).
%t A373532 f[n_] := Max[Tally[EulerPhi[Divisors[n]]][[;; , 2]]]; seq[len_, nmax_] := Module[{s = Table[0, {len}], c = 0, n = 1, i}, While[c < len && n < nmax, i = f[n]; If[i <= len && s[[i]] == 0, c++; s[[i]] = n]; n++]; s]; seq[12, 10^6]
%o A373532 (PARI) f(n) = vecmax(matreduce(apply(x->eulerphi(x), divisors(n)))[ , 2]);
%o A373532 lista(nmax, kmax = oo) = {my(v = vector(nmax), k = 1, c = 0, i); while(c < nmax && k < kmax, i = f(k); if(i <= nmax && v[i] == 0, c++; v[i] = k); k++); v}
%o A373532 (Python)
%o A373532 from collections import Counter
%o A373532 from itertools import count, islice
%o A373532 from sympy import divisors, totient
%o A373532 def agen(): # generator of terms
%o A373532     adict, n = dict(), 1
%o A373532     for k in count(1):
%o A373532         divs = divisors(k)
%o A373532         if len(divs) < n:
%o A373532             continue
%o A373532         c = Counter(totient(d) for d in divs)
%o A373532         v = c.most_common(1)[0][1]
%o A373532         if v not in adict:
%o A373532             adict[v] = k
%o A373532             while n in adict:
%o A373532                 yield adict[n]
%o A373532                 n += 1
%o A373532 print(list(islice(agen(), 11))) # _Michael S. Branicky_, Jun 08 2024
%Y A373532 Cf. A061799, A328857, A373531.
%K A373532 nonn
%O A373532 1,2
%A A373532 _Amiram Eldar_, Jun 08 2024