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A242134
Number of semiprimes with n digits.
0
3, 31, 265, 2326, 20753, 186657, 1694289, 15522934, 143361278, 1332987907, 12466213899, 117166026836, 1105962031475, 10478814259427, 99613914990801, 949727475528388, 9078425620890083, 86983554771459735, 835176988544997091, 8034305823411044844, 77423350444120266442
OFFSET
1,1
FORMULA
a(n) = A066265(n) - A066265(n-1). - Jens Kruse Andersen, Aug 16 2014
EXAMPLE
4, 6, and 9 are semiprimes with 1 digit. So a(1) = 3.
PROG
(PARI) vector(8, n, sum(k=10^(n-1), 10^n-1, bigomega(k)==2))
CROSSREFS
Sequence in context: A198852 A114849 A221899 * A221894 A198964 A212730
KEYWORD
nonn,hard,base
AUTHOR
Derek Orr, Aug 15 2014
EXTENSIONS
a(9)-a(18) from A066265, added by Jens Kruse Andersen, Aug 16 2014
a(19)-a(21) from A066265, added by Jon E. Schoenfield, Feb 10 2022
STATUS
approved