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 A089044 Numbers n such that abs(d(n) - log(n) + 1 - 2*gamma) is a decreasing sequence, where d(n) is the number of divisors A000005(n) and gamma is Euler's constant A001620. 2

%I

%S 1,3,5,7,46,2514,2522,2526,2534,2536,2542,2546,2553,2555,18873,139454,

%T 139475,7614005,7614010,7614015,7614022,7614030,7614033,7614034,

%U 7614056,7614062,7614066,7614069,7614079,7614082,7614086,7614087,7614088

%N Numbers n such that abs(d(n) - log(n) + 1 - 2*gamma) is a decreasing sequence, where d(n) is the number of divisors A000005(n) and gamma is Euler's constant A001620.

%D G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979, Theorem 320.

%H Hugo Pfoertner, <a href="/A089044/b089044.txt">Table of n, a(n) for n = 1..7613</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Euler-MascheroniConstant.html">Euler-Mascheroni Constant</a>

%e a(5)=46 because d(46) - log(46) + 1 - 2*0.5772156649... = 0.016927274... is less than

%e abs(d(7) - log(7) + 1 - 2*0.5772156649...) = abs(-0.100341479...) with d(46)=4 and d(7)=2.

%t f[n_] := N[ Abs[ DivisorSigma[0, n] - Log@ n + 1 - 2 EulerGamma], 32]; k = 1; lst = {}; mx = Infinity; While[k < 8000000, a = f@k; If[a < mx, mx = a; AppendTo[lst, k]]; k++]; lst (* _Robert G. Wilson v_, Dec 11 2017 *)

%o (PARI)

%o d=1.0;n=0;\

%o for(j=2,16,kmin=round(exp(j-2*Euler+1-2*d));kmax=round(exp(j-2*Euler+1+2*d));\

%o for(k=kmin,kmax,dd=abs(numdiv(k)-log(k)+1-2*Euler);\

%o if(dd<d,d=dd;print1(k,", "))))

%o \\ _Hugo Pfoertner_, Dec 08 2017

%Y Cf. A000005 = number of divisors of n, A001620 = Euler's constant gamma, A089084.

%K nonn

%O 1,2

%A _Leroy Quet_ and _Hugo Pfoertner_, Dec 02 2003

%E Terms beyond a(5) from _Hans Havermann_, Dec 02 2003

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Last modified May 7 19:48 EDT 2021. Contains 343652 sequences. (Running on oeis4.)