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%I #33 Jul 07 2017 03:26:58
%S 2,6,20,60,208,624,2080,6240,18720,58240,176000,529408,1593344,
%T 4780032,14344192,43040768,129138688,387416064,1162248192,3486777344,
%U 10460332032,31380996096,94142988288,282428964864,847286894592,2541860683776,7625582051328
%N The largest n-almost prime less than 3^n.
%C All terms are even as 3^n is the first odd n-almost prime.
%H Jon E. Schoenfield, <a href="/A289173/b289173.txt">Table of n, a(n) for n = 1..100</a>
%e a(26) = 2541860683776 = 3^26 - 5144553 = 2^18*3^6*47*283 (a 26-almost prime).
%e From _Michael De Vlieger_, Jun 27 2017: (Start)
%e Table of prime factors of a(n) for 1 <= n <= 16:
%e 1: 2
%e 2: 2 3
%e 3: 2 2 5
%e 4: 2 2 3 5
%e 5: 2 2 2 2 13
%e 6: 2 2 2 2 3 13
%e 7: 2 2 2 2 2 5 13
%e 8: 2 2 2 2 2 3 5 13
%e 9: 2 2 2 2 2 3 3 5 13
%e 10: 2 2 2 2 2 2 2 5 7 13
%e 11: 2 2 2 2 2 2 2 5 5 5 11
%e 12: 2 2 2 2 2 2 2 2 2 2 11 47
%e 13: 2 2 2 2 2 2 2 2 2 2 2 2 389
%e 14: 2 2 2 2 2 2 2 2 2 2 2 2 3 389
%e 15: 2 2 2 2 2 2 2 2 2 2 2 2 2 17 103
%e 16: 2 2 2 2 2 2 2 2 2 2 2 2 2 2 37 71(End)
%t Table[SelectFirst[Range[3^n - 1, 2^n, -1], PrimeOmega@ # == n &], {n, 18}] (* _Michael De Vlieger_, Jun 27 2017 *)
%o (PARI) for (n = 1,26, m = 3^n-1; while(bigomega(m) <> n, m = m-2); print1 (m ","))
%o (PARI) a(n)=my(target=n-1); forstep(k=3^n\2,1,-1, if(bigomega(k)==target, return(2*k))) \\ _Charles R Greathouse IV_, Jul 05 2017
%Y Cf. A078843 (where 3^n occurs in n-almost primes).
%K nonn
%O 1,1
%A _Zak Seidov_, Jun 26 2017
%E a(27) from _Jon E. Schoenfield_, Jul 02 2017
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