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 A053166 Smallest positive integer for which n divides a(n)^4. 13
 1, 2, 3, 2, 5, 6, 7, 2, 3, 10, 11, 6, 13, 14, 15, 2, 17, 6, 19, 10, 21, 22, 23, 6, 5, 26, 3, 14, 29, 30, 31, 4, 33, 34, 35, 6, 37, 38, 39, 10, 41, 42, 43, 22, 15, 46, 47, 6, 7, 10, 51, 26, 53, 6, 55, 14, 57, 58, 59, 30, 61, 62, 21, 4, 65, 66, 67, 34, 69, 70, 71, 6, 73, 74, 15, 38 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS According to Broughan (2002, 2003, 2006), a(n) is the "upper 4th root of n". The "lower 4th root of n" is sequence A053164. - Petros Hadjicostas, Sep 15 2019 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 Henry Bottomley, Some Smarandache-type multiplicative sequences. Kevin A. Broughan, Restricted divisor sums, Acta Arithmetica, 101(2) (2002), 105-114. Kevin A. Broughan, Relationship between the integer conductor and k-th root functions, Int. J. Pure Appl. Math. 5(3) (2003), 253-275. Kevin A. Broughan, Relaxations of the ABC Conjecture using integer k'th roots, New Zealand J. Math. 35(2) (2006), 121-136. Eric Weisstein's World of Mathematics, Smarandache Ceil Function. FORMULA a(n) = n/A000190(n) = A019554(n)/(A008835(A019554(n)^2))^(1/4). If n is 5th-power-free (i.e., not 32, 64, 128, 243, ...) then a(n) = A007947(n). Multiplicative with a(p^e) = p^(ceiling(e/4)). - Christian G. Bower, May 16 2005 MATHEMATICA f[p_, e_] := p^Ceiling[e/4]; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Sep 08 2020 *) PROG (PARI) a(n) = my(f=factor(n)); for (i=1, #f~, f[i, 2] = ceil(f[i, 2]/4)); factorback(f); \\ Michel Marcus, Jun 09 2014 CROSSREFS Cf. A000188 (inner square root), A019554 (outer square root), A053150 (inner 3rd root), A019555 (outer 3rd root), A053164 (inner 4th root), A015052 (outer 5th root), A015053 (outer 6th root). Cf. A000189, A000190, A008835, A015051. Sequence in context: A015053 A062953 A015052 * A166140 A019555 A243074 Adjacent sequences:  A053163 A053164 A053165 * A053167 A053168 A053169 KEYWORD nonn,mult AUTHOR Henry Bottomley, Feb 29 2000 STATUS approved

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Last modified April 13 00:24 EDT 2021. Contains 342934 sequences. (Running on oeis4.)