Table of n, a(n) for n=1..8.
Achim Flammenkamp, The Multiply Perfect Numbers Page,
a(n) = A001221(A007539(n))
a(4)=4 because the smallest 4-perfect number factorization is 2^5*3^3*5*7, which has 4 different prime factors.
Sequence in context: A226161 A188624 A256994 * A058521 A116628 A140463
Adjacent sequences: A107478 A107479 A107480 * A107482 A107483 A107484
Jose Brox (tautocrona(AT)terra.es), May 27 2005