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A051222 Numbers n such that Bernoulli number B_{n} has denominator 6. 42
2, 14, 26, 34, 38, 62, 74, 86, 94, 98, 118, 122, 134, 142, 146, 158, 182, 194, 202, 206, 214, 218, 254, 266, 274, 278, 298, 302, 314, 326, 334, 338, 362, 386, 394, 398, 422, 434, 446, 454, 458, 482, 494, 514, 518, 526, 538, 542, 554, 566, 578 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Alternative definition: let D(m) = set of divisors of m; sequence gives n such that the set 1 + D(n) contains only two primes, 2 and 3. E.g., n=98: D(98)={1,2,7,15,49,98}, 1+D = {2,3,8,16,50,99} of which only 2 terms are prime numbers: {2,3}. Observation by Labos Elemer, Jun 24 2002. This is a consequence of the von Staudt-Clausen theorem. - N. J. A. Sloane, Jan 04 2004

The fraction of Bernoulli numbers with denominator 6 is roughly 1/6, see Erdős-Wagstaff. But calculations by H. Cohen and G. Tenenbaum suggest that the fraction is closer to 1/7 (posting to Number Theory List around Dec 20 2005).

Simon Plouffe reports (Feb 13 2007) that at B_{9083002} the proportion is 0.151848915149418661363281... and still decreasing very slowly.

In his PhD thesis at the University of Illinois (see reference), Richard Sunseri proved that a higher proportion of Bernoulli denominators equal 6 than any other value.

Numerator(B_{n}) mod Denominator(B_{n}) = 1. This relation stands also for B_{n} with denominator equal to 1, 2, 42 and 1806 (A014117). - Paolo P. Lava, Mar 30 2015

Rado showed that for a given Bernoulli number B_n there exist infinitely many Bernoulli numbers B_m having the same denominator. As a special case, if n = 2p where p is an odd prime p == 1 (mod 3), then the denominator of the Bernoulli number B_n equals 6. - Bernd C. Kellner, Mar 21 2018

REFERENCES

B. C. Berndt, Ramanujan's Notebooks Part IV, Springer-Verlag, see p. 75.

K. L. Jensen, Om talteoretiske Egenskaber ved de Bernoulliske Tal, Nyt Tidsskrift Für Mathematik, Afdeling B, vol. 28 (1915), pp. 73-83.

C. J. Moreno and S. S. Wagstaff, Sums of Squares of Integers, CRC Press, 2005, Sect. 3.9.

H. Rademacher, Topics in Analytic Number Theory, Springer, 1973, Chap. 1, p. 10.

Richard Sunseri, p-Adic L-functions and densities relating to Bernoulli numbers, PhD thesis, University of Illinois, 1979.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

Paul Erdős and Samuel S. Wagstaff, Jr., The fractional parts of the Bernoulli numbers, Illinois J. Math. 24 (1980), pp. 104-112, MR 81c:10064.

R. Rado, A note on the Bernoullian numbers, J. London Math. Soc. 9 (1934) 88-90.

Index entries for sequences related to Bernoulli numbers.

MATHEMATICA

di[x_] := Divisors[x]

dp[x_] := Part[di[x], Flatten[Position[PrimeQ[1+di[x]], True]]]+1

Do[s=Length[dp[n]]; If[Equal[s, 2], Print[n]], {n, 1, 10000}] (* Labos Elemer *)

Do[s=Denominator[BernoulliB[n]]; If[Equal[s, 6], Print[n]], {n, 1, 1000}] (* Labos Elemer *)

Do[s=1+Divisors[n]; s1=Flatten[Position[PrimeQ[s], True]]; (*analogous [suitably modified] pairs of programs yield A051225-A051230*) s2=Part[s, s1]; If[Equal[s2, {2, 3}], Print[n]], {n, 1, 100}] (* Labos Elemer *)

Select[Range[600], Denominator[BernoulliB[#]]==6&] (* Harvey P. Dale, Dec 08 2011 *)

PROG

(PARI) for(n=1, 10^3, if(denominator(bernfrac(n))==6, print1(n, ", "))); \\ Joerg Arndt, Oct 28 2014

(PARI) is(n)=if(n%2, return(0)); fordiv(n/2, d, if(isprime(2*d+1)&&d>1, return(0))); 1 \\ Charles R Greathouse IV, Oct 28 2014

CROSSREFS

Except for 2, all terms are even nontotient numbers. Proper subset of A005277: e.g., 50 and 90 are not here. - Labos Elemer

A112772 is a subsequence. - Bernd C. Kellner, Mar 21 2018

Cf. A045979, A000005, A067513, A002202, A005277.

Sequence in context: A109255 A285990 A174594 * A194411 A017545 A280268

Adjacent sequences:  A051219 A051220 A051221 * A051223 A051224 A051225

KEYWORD

nonn,nice,easy

AUTHOR

N. J. A. Sloane

EXTENSIONS

Additional comments and references from Sam Wagstaff, Dec 20 2005

STATUS

approved

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Last modified March 23 14:17 EDT 2019. Contains 321431 sequences. (Running on oeis4.)