A218245 - OEIS

A218245

Nicolas's sequence, whose nonnegativity is equivalent to the Riemann hypothesis.

2, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

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OFFSET

1,1

COMMENTS

a(n) = floor(p(n)#/phi(p(n)#) - log(log(p(n)#))*exp(gamma)), where p(n)# is the n-th primorial, phi is Euler's totient function, and gamma is Euler's constant.

J.-L. Nicolas proved that all terms are >= 0 if and only if the Riemann hypothesis (RH) is true. In fact, results in his 2012 paper imply that RH is equivalent to a(n) = 0 for n > 6. Nicolas's refinement of this result is in A233825.

He also proved that if RH is false, then infinitely many terms are >= 0 and infinitely many terms are < 0.

See Nicolas's sequence A216868 for references, links, and additional cross-refs.

LINKS

Table of n, a(n) for n=1..97.

FORMULA

a(n) = [p(n)#/phi(p(n)#) - log(log(p(n)#))*exp(gamma)].

a(n) = [A002110(n)/A005867(n) - log(log(A002110(n)))*e^gamma].

EXAMPLE

p(2)# = 2*3 = 6 and phi(6) = 2, so a(2) = [6/2 - log(log(6))*e^gamma] = [3-0.58319...*1.78107...] = [3-1.038...] = 1.

MATHEMATICA

primorial[n_] := Product[Prime[k], {k, n}]; Table[ With[{p = primorial[n]}, Floor[N[p/EulerPhi[p] - Log[Log[p]]*Exp[EulerGamma]]]], {n, 1, 100}]

CROSSREFS

Cf. A216868, A233825.

Sequence in context: A165105 A325674 A055641 * A352516 A086075 A316865

Adjacent sequences: A218242 A218243 A218244 * A218246 A218247 A218248

KEYWORD

nonn

AUTHOR

Jonathan Sondow, Oct 24 2012

STATUS

approved