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1,2
a(n) = A000079(A032741(n)).
Also number of subsets of divisors of n which do not contain 1; thus a(n) = (A100587(n)+1)/2. - Vladeta Jovovic, Jul 02 2007
Antti Karttunen, Table of n, a(n) for n = 1..10000
a(n) = 2^(A000005(n)-1).
a(12) = #{{1}, {3}, {1,2}, {1,4}, {2,3}, {1,6}, {3,4}, {1,2,4}, {3,6}, {1,2,6}, {2,3,4}, {1,4,6}, {2,3,6}, {1,12}, {3,4,6}, {1,2,4,6}, {3,12}, {1,2,12}, {2,3,4,6}, {1,4,12}, {2,3,12}, {1,6,12}, {3,4,12}, {1,2,4,12}, {3,6,12}, {1,2,6,12}, {2,3,4,12}, {1,4,6,12}, {2,3,6,12}, {1,2,4,6,12}, {3,4,6,12}, {2,3,4,6,12}} = 32.
(PARI) a(n)=2^(numdiv(n)-1) \\ Charles R Greathouse IV, Jan 19 2017
Cf. A000005, A000079, A001227, A032741, A100587.
Sequence in context: A270366 A072478 A190014 * A018818 A157019 A067538
Adjacent sequences: A100574 A100575 A100576 * A100578 A100579 A100580
nonn,easy,changed
Reinhard Zumkeller, Nov 29 2004
approved