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Jon E. Schoenfield, Table of n, a(n) for n = 0..30
(3!)! = 6! = 720 has ten binary digits (1011010000), so a(3) = 10.
(PARI) a(n) = length(binary(n!!)) \\ Michel Marcus, Jun 02 2013
Sequence in context: A245903 A100248 A108486 * A003578 A274276 A152600
Adjacent sequences: A152165 A152166 A152167 * A152169 A152170 A152171
Jon E. Schoenfield, Nov 27 2008