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 A061391 t(n,3) = Sum_{d|n} tau(d^3), where tau(n) = number of divisors of n, cf. A000005. 5
 1, 5, 5, 12, 5, 25, 5, 22, 12, 25, 5, 60, 5, 25, 25, 35, 5, 60, 5, 60, 25, 25, 5, 110, 12, 25, 22, 60, 5, 125, 5, 51, 25, 25, 25, 144, 5, 25, 25, 110, 5, 125, 5, 60, 60, 25, 5, 175, 12, 60, 25, 60, 5, 110, 25, 110, 25, 25, 5, 300, 5, 25, 60, 70, 25, 125, 5, 60, 25, 125, 5, 264 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Inverse Mobius transform of A048785. - R. J. Mathar, Feb 09 2011 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA t(n, k) = Sum_{d|n} tau(d^k) is multiplicative: if the canonical factorization of n = Product p^e(p) over primes then t(n, k) = Product t(p^e(p), k), t(p^e(p), k) = (1/2) *(k*e(p)+2)*(e(p)+1). a(n) = sum( d dividing n, tau(nd)) - Benoit Cloitre, Nov 30 2002 Multiplicative with a(p^e) = (e+6 choose e). Mitch Harris Jun 27, 2005. sum(n=1,infinity,tau(n^3)*x^n/(1-x^n)). EXAMPLE For k=2 we get an interesting identity: Sum_{d|n} tau(d^2)=(tau(n))^2, cf. A048691, A035116. PROG (PARI) A061391 = n -> sumdiv(n, d, numdiv(d^3)); for(n=1, 10000, write("b061391.txt", n, " ", A061391(n))); \\ Antti Karttunen, Jan 17 2017 CROSSREFS Cf. t(n, 0) = A000005(n), t(n, 1) = A007425(n), t(n, 2) = A035116(n). Sequence in context: A098331 A222575 A222681 * A168336 A123133 A302676 Adjacent sequences:  A061388 A061389 A061390 * A061392 A061393 A061394 KEYWORD nonn,mult AUTHOR Vladeta Jovovic, Apr 29 2001 STATUS approved

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Last modified January 20 14:40 EST 2019. Contains 319333 sequences. (Running on oeis4.)