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 A163108 a(n) = sigma(tau(sigma(n))). 1
 1, 3, 4, 3, 7, 12, 7, 7, 3, 12, 12, 12, 7, 15, 15, 3, 12, 7, 12, 15, 12, 13, 15, 28, 3, 15, 15, 15, 15, 28, 12, 12, 18, 15, 18, 7, 7, 28, 15, 28, 15, 28, 12, 28, 15, 28, 18, 12, 7, 7, 28, 12, 15, 31, 28, 31, 18, 28, 28, 31, 7, 28, 15, 3, 28, 24, 12, 28, 28, 24, 28, 15, 7, 15, 12, 28, 28 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Repeated application of tau (number of divisors) and sigma (sum of divisors). LINKS Antti Karttunen, Table of n, a(n) for n = 1..16384 FORMULA a(n) = A000203(A000005(A000203(n))) = A000203(A062068(n)) = A062069(A000203(n)). MAPLE with(numtheory) : A163108 := proc(n) sigma(tau(sigma(n))) ; end: seq(A163108(n), n=1..120) ; # R. J. Mathar, Jul 27 2009 PROG (PARI) A163108(n) = sigma(numdiv(sigma(n))); \\ Antti Karttunen, Nov 18 2017 CROSSREFS Cf. A000005, A000203, A062068, A062069, A163107. Sequence in context: A127737 A299416 A333974 * A077005 A328347 A265723 Adjacent sequences:  A163105 A163106 A163107 * A163109 A163110 A163111 KEYWORD nonn AUTHOR Jaroslav Krizek, Jul 20 2009 EXTENSIONS More terms from R. J. Mathar, Jul 27 2009 STATUS approved

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Last modified July 27 01:13 EDT 2021. Contains 346300 sequences. (Running on oeis4.)