%I
%S 1,2,4,6,12,16,30,36,48,60,64,144,180,192,210,240,420,576,720,900,960,
%T 1024,1260,1296,1680,2310,2880,3072,3600,4096,4620,5040,5184,6300,
%U 6480,6720,9216,12288,13860,14400
%N Products of primorials where all exponents in its prime factorization are one less than a prime.
%C Erdős & Mirsky call these Bnumbers.
%H Amiram Eldar, <a href="/A220219/b220219.txt">Table of n, a(n) for n = 1..10000</a>
%H P. Erdős and L. Mirsky, <a href="http://www.renyi.hu/~p_erdos/195212.pdf">The distribution of values of the divisor function d(n)</a>, Proc. London Math. Soc. 2 (1952), pp. 257271.
%F Erdős & Mirsky show that there are exp((k + o(1)) sqrt(log x)/log log x) members of this sequence below x, where k = Pi * sqrt(8/3) = 5.130....
%o (PARI) is(n)=my(e=valuation(n,2),e1); if(!isprime(e+1), return(n==1)); n>>=e; forprime(p=3,, if(n==1, return(1)); e1=valuation(n,p); if(!isprime(e1+1)  e1 > e, return(0)); n/=p^e1; e = e1)
%Y Intersection of A025487 and A220218.
%K nonn
%O 1,2
%A _Charles R Greathouse IV_, Dec 07 2012
