A291144 a(n) is the smallest number k such that psi(k) = A001615(k) is the product of n distinct primes.

2, 4, 25, 218, 1538, 20018, 570569, 9869858, 148728578, 7865117258, 198255197138, 5481986730218, 235725429399458, 12372844050106538, 587192044634054858, 32820287260716215258, 1325292444739061819018, 91010656573966064915978, 8683441125519459364805738

Offset

1,1

Links

Table of n, a(n) for n=1..19.

Example

a(4) = 218 = 2*109 because psi(2*109) = 2*3*5*11 and 218 is the least number with this property.

Prog

(PARI) a001615(n) = n*sumdivmult(n, d, issquarefree(d)/d);
a(n) = {my(k = 1); while (!issquarefree(a001615(k)) || bigomega(a001615(k)) != n, k++); k; }
(PARI) v=vector(100); forfactored(k=2, 10^9, f=factor(A001615(k[1], k[2]))[, 2]; if(vecmax(f)==1 && (#f)<=#v && v[#f]==0, v[#f]=k[1]; print(#f" "k[1]))) \\ Charles R Greathouse IV, Aug 19 2017

Crossrefs

Cf. A001615.

Sequence in context: A266495 A365097 A119029 * A162120 A162121 A162122

Adjacent sequences: A291141 A291142 A291143 * A291145 A291146 A291147

Keyword

nonn

Author

Altug Alkan, Aug 18 2017

Extensions

a(10) from Charles R Greathouse IV, Aug 19 2017

a(11)-a(19) from Giovanni Resta, Aug 21 2017

Status

approved