1,1

28 is member because the number of proper divisors of 28 is 5, a prime number.

Cf. A000396, A032741, A133033, A154896.

Sequence in context: A038182 A095723 A057246 this_sequence A074849 A100874 A156927

Adjacent sequences: A154892 A154893 A154894 this_sequence A154896 A154897 A154898

more,nonn

Omar E. Pol (info(AT)polprimos.com), Jan 25 2009