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 A338172 a(n) is the product of those divisors d of n such that tau(d) divides sigma(d). 3
 1, 1, 3, 1, 5, 18, 7, 1, 3, 5, 11, 18, 13, 98, 225, 1, 17, 18, 19, 100, 441, 242, 23, 18, 5, 13, 81, 98, 29, 40500, 31, 1, 1089, 17, 1225, 18, 37, 722, 1521, 100, 41, 1555848, 43, 10648, 10125, 1058, 47, 18, 343, 5, 2601, 13, 53, 26244, 3025, 5488, 3249, 29 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n) is the product of arithmetic divisors d of n. a(n) = pod(n) = A007955(n) for numbers n from A334420. LINKS FORMULA a(p) = p for odd primes p (A065091). EXAMPLE a(6) = 18 because there are 3 aritmetic divisors of 6 (1, 3 and 6): sigma(1)/tau(1) =  1/1 = 1; sigma(3)/tau(3) = 4/2 = 2; sigma(6)/tau(6) = 12/4 = 3. Product of this divisors is 18. MATHEMATICA a[n_] := Times @@ Select[Divisors[n],  Divisible[DivisorSigma[1, #], DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, Oct 15 2020 *) PROG (MAGMA) [&*[d: d in Divisors(n) | IsIntegral(&+Divisors(d) / #Divisors(d))]: n in [1..100]] (PARI) a(n) = my(d=divisors(n)); prod(k=1, #d, if (sigma(d[k]) % numdiv(d[k]), 1, d[k])); \\ Michel Marcus, Oct 15 2020 CROSSREFS Cf. A000005 (tau), A000203 (sigma), A003601 (arithmetic numbers). Cf. A334420, A334421. See A338170 and A338171 for number and sum of such divisors. Sequence in context: A181836 A124740 A073597 * A104053 A187369 A039512 Adjacent sequences:  A338169 A338170 A338171 * A338173 A338174 A338175 KEYWORD nonn AUTHOR Jaroslav Krizek, Oct 14 2020 STATUS approved

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Last modified June 13 20:25 EDT 2021. Contains 345009 sequences. (Running on oeis4.)