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A138221
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a(n) = the smallest divisor of n that is >= the number of positive divisors of n.
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4
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1, 2, 3, 4, 5, 6, 7, 4, 3, 5, 11, 6, 13, 7, 5, 8, 17, 6, 19, 10, 7, 11, 23, 8, 5, 13, 9, 7, 29, 10, 31, 8, 11, 17, 5, 9, 37, 19, 13, 8, 41, 14, 43, 11, 9, 23, 47, 12, 7, 10, 17, 13, 53, 9, 5, 8, 19, 29, 59, 12, 61, 31, 7, 8, 5, 11, 67, 17, 23, 10, 71, 12, 73, 37, 15, 19, 7, 13, 79, 10, 9
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OFFSET
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1,2
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LINKS
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FORMULA
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EXAMPLE
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There are four positive divisors of 15: (1,3,5,15). The smallest of these divisors that is >=4 is 5; so a(15) = 5.
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MAPLE
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with(numtheory): a:=proc(n) local dn, i: dn:=divisors(n): for i while dn[i] < tau(n) do end do: dn[i] end proc: seq(a(n), n=1..60); # Emeric Deutsch, Mar 17 2008
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MATHEMATICA
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f[n_] := First@Select[Divisors@n, # >= DivisorSigma[0, n] &]; Array[f, 81] (* Robert G. Wilson v *)
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PROG
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(PARI) a(n) = {my(d = divisors(n), nd = #d); for(i = 1, nd, if(d[i] >= nd, return(d[i]))); } \\ Amiram Eldar, Apr 15 2024
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CROSSREFS
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KEYWORD
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nonn,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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