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 A057661 a(n) = Sum_{k=1..n} lcm(n,k)/n. 25
 1, 2, 4, 6, 11, 11, 22, 22, 31, 32, 56, 39, 79, 65, 74, 86, 137, 92, 172, 116, 151, 167, 254, 151, 261, 236, 274, 237, 407, 221, 466, 342, 389, 410, 452, 336, 667, 515, 550, 452, 821, 452, 904, 611, 641, 761, 1082, 599, 1051, 782, 956, 864, 1379, 821, 1166 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sum of numerators of n-th order Farey series (cf. A006842). - Benoit Cloitre, Oct 28 2002 Equals row sums of triangle A143613. - Gary W. Adamson, Aug 27 2008 Equals row sums of triangle A159936. - Gary W. Adamson, Apr 26 2009 Also row sums of triangle A164306. - Reinhard Zumkeller, Aug 12 2009 REFERENCES H. W. Gould and Temba Shonhiwa, Functions of GCD's and LCM's, Indian J. Math. (Allahabad), 39 (1997), 11-35. H. W. Gould and Temba Shonhiwa, A generalization of Cesaro's function and other results, Indian J. Math. (Allahabad), 39 (1997), 183-194. LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 FORMULA a(n) = (1+A057660(n))/2. a(n) = A051193(n)/n. a(n) = a(n) = Sum_{d|n} psi(d), where psi(m) = is the sum of totatives of m (A023896). - Jaroslav Krizek, Dec 28 2016 a(n) = Sum_{i=1..n} denominator(n/i). - Wesley Ivan Hurt, Feb 26 2017 G.f.: x/(2*(1 - x)) + (1/2)*Sum_{k>=1} k*phi(k)*x^k/(1 - x^k), where phi() is the Euler totient function (A000010). - Ilya Gutkovskiy, Aug 31 2017 If p is prime, then a(p) = T(p-1) + 1 = p(p-1)/2 + 1, where T(n) = n(n+1)/2 is the n-th triangular number (A000217). - David Terr, Feb 10 2019 MATHEMATICA Table[Total[Numerator[Range[n]/n]], {n, 55}] (* Alonso del Arte, Oct 07 2011 *) PROG (Haskell) a057661 n = a051193 n `div` n  -- Reinhard Zumkeller, Jun 10 2015 (MAGMA) [&+[&+[h: h in [1..d] | GCD(h, d) eq 1]: d in Divisors(n)]: n in [1..100]]; // Jaroslav Krizek, Dec 28 2016 (PARI) a(n)=sum(k=1, n, lcm(n, k))/n \\ Charles R Greathouse IV, Feb 07 2017 CROSSREFS Cf. A000010, A000217, A018804, A051193, A057660, A143613, A159936. See A341316 for another version. Sequence in context: A304532 A279911 A063183 * A237277 A097954 A324333 Adjacent sequences:  A057658 A057659 A057660 * A057662 A057663 A057664 KEYWORD easy,nice,nonn AUTHOR Henry Gould, Oct 15 2000 EXTENSIONS More terms from James A. Sellers, Oct 16 2000 STATUS approved

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Last modified April 20 11:30 EDT 2021. Contains 343135 sequences. (Running on oeis4.)