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A306759 Decimal expansion of the sum of reciprocals of Brazilian primes, also called the Brazilian primes constant. 0
3, 3, 1, 7, 5, 4, 4, 6, 6 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

The name "constant of Brazilian primes" is used in the article "Les nombres brésiliens" in link, théorème 4, page 36. Brazilian primes are in A085104.

Let S(k) be the sum of reciprocals of Brazilian primes < k. These values below come from different calculations by Jon, Michel, Daniel and Davis.

   q            S(10^q)

  ==    ========================

   1    0.1428571428571428571...  (= 1/7)

   2    0.2889927283868234859...

   3    0.3229022355626914481...

   4    0.3295236806353669357...

   5    0.3312171311946179843...

   6    0.3316038696349217289...

   7    0.3317139158654747333...

   8    0.3317434191078170412...

   9    0.3317513267394988538...

  10    0.3317535651668937256...

  11    0.3317542057931842329...

  12    0.3317543906772274268...

  13    0.3317544444033188051...

  14    0.3317544601136967527...

  15    0.3317544647354485208...

  16    0.3317544661014868080...

  17    0.3317544665073451951...

  18    0.3317544666282877863...

  19    0.3317544666644601817...

  20    0.3317544666753095766...

According to the Goormaghtigh conjecture, there are only two Brazilian primes which are twice Brazilian: 31 = (111)_5 = (11111)_2 and 8191 = (111)_90 = (1111111111111)_2. The reciprocals of these two numbers are counted only once in the sum.

REFERENCES

Daniel Lignon, Dictionnaire de (presque) tous les nombres entiers, Ellipses, Paris, 2012, page 175.

LINKS

Table of n, a(n) for n=0..8.

Bernard Schott, Les nombres brésiliens, Quadrature, no. 76, avril-juin 2010, pages 30-38; included here with permission from the editors of Quadrature.

Wikipedia, Goormaghtigh conjecture.

FORMULA

Equals Sum_{n>=1} 1/A085104(n).

EXAMPLE

1/7 + 1/13 + 1/31 + 1/43 + 1/73 + 1/127 + 1/157 + ... = 0.33175...

PROG

(PARI) brazil(N, L=List())=forprime(K=3, #binary(N+1)-1, for(n=2, sqrtnint(N-1, K-1), if(isprime((n^K-1)/(n-1)), listput(L, (n^K-1)/(n-1))))); Set(L);

brazilcons(lim, nbd) = r=brazil(10^lim); x=sum(M=1, #r, 1./r[M]); for(n=1, nbd, print1(floor(x*10^n)%10, ", ")); \\ Davis Smith, Mar 10 2019

(PARI) cons(lim)=my(v=List(), t, k); for(n=2, sqrt(lim), t=1+n; k=1; while((t+=n^k++)<=lim, if(isprime(t), listput(v, t)))); v = vecsort(Vec(v), , 8); sum(k=1, #v, 1./v[k]); \\ Michel Marcus, Mar 11 2019

CROSSREFS

Cf. A085104 (Brazilian primes), A002383 (Brazilian primes (111)_b), A225148 (Brazilian primes of the form (b^q-1)/(b-1) with q prime >= 5).

Cf. A173898 (sum of the reciprocals of the Mersenne primes), A065421 (Brun's constant).

Sequence in context: A049323 A322148 A084144 * A214362 A180735 A116401

Adjacent sequences:  A306756 A306757 A306758 * A306760 A306761 A306762

KEYWORD

nonn,more,cons

AUTHOR

Bernard Schott, Mar 08 2019

STATUS

approved

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Last modified February 24 06:06 EST 2020. Contains 332199 sequences. (Running on oeis4.)