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A220219
Products of primorials where all exponents in its prime factorization are one less than a prime.
2
1, 2, 4, 6, 12, 16, 30, 36, 48, 60, 64, 144, 180, 192, 210, 240, 420, 576, 720, 900, 960, 1024, 1260, 1296, 1680, 2310, 2880, 3072, 3600, 4096, 4620, 5040, 5184, 6300, 6480, 6720, 9216, 12288, 13860, 14400
OFFSET
1,2
COMMENTS
Erdős & Mirsky call these B-numbers.
LINKS
P. Erdős and L. Mirsky, The distribution of values of the divisor function d(n), Proc. London Math. Soc. 2 (1952), pp. 257-271.
FORMULA
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....
PROG
(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)
CROSSREFS
Intersection of A025487 and A220218.
Sequence in context: A098895 A266543 A330711 * A284456 A233968 A120453
KEYWORD
nonn
AUTHOR
STATUS
approved