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 A070919 a(n) = Card{ (x,y,z) | lcm(x,y,z)=n }. 8
 1, 7, 7, 19, 7, 49, 7, 37, 19, 49, 7, 133, 7, 49, 49, 61, 7, 133, 7, 133, 49, 49, 7, 259, 19, 49, 37, 133, 7, 343, 7, 91, 49, 49, 49, 361, 7, 49, 49, 259, 7, 343, 7, 133, 133, 49, 7, 427, 19, 133, 49, 133, 7, 259, 49, 259, 49, 49, 7, 931, 7, 49, 133, 127, 49, 343, 7, 133 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A048691(n) gives Card{ (x,y) | lcm(x,y)=n }. LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 O. Bagdasar, On some functions involving the lcm and gcd of integer tuples, Scientific Publications of the State University of Novi Pazar, Appl. Maths. Inform. and Mech., Vol. 6, 2 (2014), 91-100. FORMULA a(n) = Sum_{d|n} A000005(d)^3*A008683(n/d). Sum_{k>0} a(k)/k^s = (1/zeta(s))*Sum_{k>0} tau(k)^3/k^s. Multiplicative with a(p^e) = 1+3*e+3*e^2 for prime p and e >= 0. - Werner Schulte, Nov 30 2018 MATHEMATICA Join[{1}, Table[Product[(k + 1)^3 - k^3, {k, FactorInteger[n][[All, 2]]}], {n, 2, 68}]] (* Geoffrey Critzer, Jan 10 2015 *) PROG (PARI) for(n=1, 100, print1(sumdiv(n, d, numdiv(d)^3*moebius(n/d)), ", ")) (PARI) a(n) = vecprod(apply(x->(x+1)^3-x^3, factor(n)[, 2])); \\ Amiram Eldar, Sep 03 2023 CROSSREFS Cf. A000005, A008683, A048691, A070920, A070921, A086222, A247513. Sequence in context: A196395 A358380 A139126 * A070847 A195863 A053416 Adjacent sequences: A070916 A070917 A070918 * A070920 A070921 A070922 KEYWORD mult,easy,nonn AUTHOR Benoit Cloitre, May 20 2002 STATUS approved

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Last modified August 10 13:06 EDT 2024. Contains 375056 sequences. (Running on oeis4.)