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 A089226 Smallest composite number with exactly n 1's in binary representation. 3
 4, 6, 14, 15, 55, 63, 247, 255, 511, 1023, 2047, 4095, 12287, 16383, 32767, 65535, 196607, 262143, 983039, 1048575, 2097151, 4194303, 8388607, 16777215, 33554431, 67108863, 134217727, 268435455, 536870911, 1073741823, 3221225471 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A000120(a(n)) = n; A023416(a(n)) <= 1 for n>1. - Ray Chandler, Feb 15 2004 a(n) = A000225(n) unless n is in A000043. - Robert Israel, Jun 20 2019 LINKS Robert Israel, Table of n, a(n) for n = 1..3318 MAPLE f:= proc(n) local i, t;   for i from n to 0 by -1 do     t:= 2^(n+1) - 2^i - 1;     if not isprime(t) then return t fi   od end proc: f(1):= 4: map(f, [\$1..100]); # Robert Israel, Jun 20 2019 CROSSREFS Cf. A000043, A000120, A000225, A023416, A061712. Sequence in context: A310617 A305842 A094298 * A102029 A310618 A310619 Adjacent sequences:  A089223 A089224 A089225 * A089227 A089228 A089229 KEYWORD nonn AUTHOR Reinhard Zumkeller, Dec 10 2003 EXTENSIONS More terms from Ray Chandler, Feb 15 2004 STATUS approved

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Last modified February 20 14:03 EST 2020. Contains 332078 sequences. (Running on oeis4.)