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 A216957 a(1)=2; for n > 1, a(n) = 2^(n-2) + (1/(2n-2)) * Sum_{ d divides n-1 } phi(2d)*2^((n-1)/d). 2
 2, 2, 4, 6, 12, 20, 40, 74, 148, 286, 568, 1118, 2228, 4412, 8788, 17480, 34836, 69392, 138388, 275942, 550560, 1098516, 2192572, 4376666, 8738324, 17448308, 34845304, 69594398, 139011816, 277691852, 554767744, 1108378658, 2214594580, 4425117884, 8842583584, 17670722600, 35314182976, 70576759892, 141055781836 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..1000 MAPLE with(numtheory); f:=n-> if n=1 then 2 else 2^(n-2) + (1/(2*n-2)) * add(phi(2*d)*2^((n-1)/d), d in divisors(n-1)); fi; CROSSREFS Different from, but easily confused with, A003000 and A122536. Sequence in context: A030435 A063886 A003000 * A122536 A238014 A052953 Adjacent sequences:  A216954 A216955 A216956 * A216958 A216959 A216960 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 26 2012 STATUS approved

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Last modified August 12 11:44 EDT 2020. Contains 336439 sequences. (Running on oeis4.)