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A073087
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Least k such that sigma(k^k)>=n*k^k.
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2
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OFFSET
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1,2
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COMMENTS
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Does a(n) = the product of primes less than or equal to prime(n+1) = A002110(n+1)? Answer from Lambert Klasen (Lambert.Klasen(AT)gmx.net), Sep 14 2005: No, this is not true.
Note that sigma(k^k) = prod (p^(k r + 1) - 1)/(p - 1). - Mitch Harris, Sep 14 2005
I have proved to my own satisfaction that for n >= 4, A073087(n) = p#, where p is the smallest prime satisfying p#/phi(p#) >= n. See link. - David W. Wilson, Sep 14 2005
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LINKS
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FORMULA
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PROG
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(PARI) a(n)=if(n<0, 0, s=1; while(sigma(s^s)<n*s^s, s++); s)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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