This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A220219 #7 Jun 21 2019 11:19:43 %S A220219 1,2,4,6,12,16,30,36,48,60,64,144,180,192,210,240,420,576,720,900,960, %T A220219 1024,1260,1296,1680,2310,2880,3072,3600,4096,4620,5040,5184,6300, %U A220219 6480,6720,9216,12288,13860,14400 %N A220219 Products of primorials where all exponents in its prime factorization are one less than a prime. %C A220219 Erdős & Mirsky call these B-numbers. %H A220219 Amiram Eldar, <a href="/A220219/b220219.txt">Table of n, a(n) for n = 1..10000</a> %H A220219 P. Erdős and L. Mirsky, <a href="http://www.renyi.hu/~p_erdos/1952-12.pdf">The distribution of values of the divisor function d(n)</a>, Proc. London Math. Soc. 2 (1952), pp. 257-271. %F A220219 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 A220219 (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 A220219 Intersection of A025487 and A220218. %K A220219 nonn %O A220219 1,2 %A A220219 _Charles R Greathouse IV_, Dec 07 2012