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 A049690 a(n) = Sum_{k=1..n} phi(2*k), where phi = Euler totient function, cf. A000010. 6
 0, 1, 3, 5, 9, 13, 17, 23, 31, 37, 45, 55, 63, 75, 87, 95, 111, 127, 139, 157, 173, 185, 205, 227, 243, 263, 287, 305, 329, 357, 373, 403, 435, 455, 487, 511, 535, 571, 607, 631, 663, 703, 727, 769, 809, 833, 877, 923, 955, 997, 1037, 1069, 1117, 1169, 1205 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Nathaniel Johnston, Table of n, a(n) for n = 0..10000 MAPLE A049690 := proc(n) return add(numtheory[phi](2*k), k=1..n): end: seq(A049690(n), n=0..54); # Nathaniel Johnston, May 24 2011 MATHEMATICA A049690[0]:=0; A049690[n_]:=A049690[n-1]+EulerPhi[2n]; Array[A049690, 200, 0] (* Enrique Pérez Herrero, Feb 25 2012 *) PROG (PARI) a(n)=sum(k=1, n, eulerphi(2*k)) \\ Charles R Greathouse IV, Feb 19 2013 CROSSREFS a(n)=b(2n), where b=A049689. Bisections: A099958, A190815. Sequence in context: A185170 A211340 A061571 * A080075 A007664 A215812 Adjacent sequences:  A049687 A049688 A049689 * A049691 A049692 A049693 KEYWORD nonn AUTHOR EXTENSIONS More terms from Vladeta Jovovic, May 18 2001 STATUS approved

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Last modified May 19 20:41 EDT 2019. Contains 323410 sequences. (Running on oeis4.)