A348053 -id:A348053 - cp's OEIS frontend

A210439 The minimal Skewes number for prime n-tuplets.

1369391, 337867, 1172531, 21432401, 251331775687, 7572964186421, 1203255673037261

Offset: 2

Alexei Kourbatov, Jan 20 2013

More formally: the least prime in the prime n-tuplet at which for the first time pi_n(p) > C_n*Li_n(p). Here pi_n(p) is the n-tuplet counting function; C_n is the Hardy-Littlewood constant, and Li_n(x) is the integral from 2 to x of (1/(log t)^n) dt.
If, for a given n, there is more than one type of n-tuplets, then a(n) is determined by the n-tuplet type for which the first sign change of pi_n - C_n*Li_n occurs earlier than for the other type(s).
For the special case n=1, the term a(1) is the Skewes number, i.e., the first prime p for which pi(p) > Li(p). The term a(1) is not included in the sequence because it is not precisely known.

			Initially, for twin primes we have pi_2(p) < C_2 Li_2(p). The inequality is reversed for the first time for the 10744th pair of twin primes (1369391,1369393), therefore a(2) = 1369391.
Similarly, for prime triples (p,p+4,p+6), pi_3(p) < C_3 Li_3(p) until the 652nd triple (337867,337871,337873) where the inequality is reversed for the first time. Thus a(3)=337867. (The reversal for the other type of triples (p,p+2,p+6) occurs much later, so triples (p,p+2,p+6) do not contribute a term to this sequence.)
From _Hugo Pfoertner_, Aug 26 2021, Oct 24 2021: (Start)
a(8) corresponds to the 134292-th 8-tuple of the form p + [0, 2, 6, 8, 12, 18, 20, 26], found using a program provided by _Norman Luhn_. This type of 8-tuple is the one that leads to the earliest crossing of the corresponding comparison value (see linked illustration), while the other two possible configurations (enumerated in A022012 and A022013 or in A346997 and A346998) are still far from crossing their respective applicable comparison values. The other two possible 8-tuples, which lead to the crossing that occurs later, determine the terms A332493(8) and A348053(8), dependent on the criterion applied to decide what is "later". (End)

Tony Forbes and Norman Luhn, Patterns of prime k-tuplets & the Hardy-Littlewood constants.
Tony Forbes and Norman Luhn, Prime k-tuplets.
Alexei Kourbatov, PARI code for computing a(6)
Norman Luhn, Database of the smallest prime k-tuplets, compressed files.
Hugo Pfoertner, Illustration of 8-tuplet counts determining a(8).
László Tóth, On The Asymptotic Density Of Prime k-tuples and a Conjecture of Hardy and Littlewood, arXiv:1910.02636 [math.NT], 2019.
Eric Weisstein's World of Mathematics, k-Tuple Conjecture
Eric Weisstein's World of Mathematics, Prime Constellation
Marek Wolf, The Skewes number for twin primes: counting sign changes of Pi_2(x)-C_2 Li_2(x), arXiv:1107.2809 [math.NT], 2011.

Cf. A052435 (round(li(n)-pi(n)), where li is the logarithmic integral and pi(x) is the prime counting function).
Cf. A332493, A333586, A333587, A348053.
Cf A022011, A022012, A022013, A346996, A346997, A346998 (related to 8-tuplets).

PARI
```
\\ See Alexei Kourbatov link.
```

a(7) from Hugo Pfoertner, May 09 2020

a(8) from Hugo Pfoertner, Aug 26 2021

A332493 The minimal Skewes number for prime n-tuplets, choosing the n-tuplet with latest occurrence of the first sign change relative to the Hardy-Littlewood prediction when more than one type of n-tuplets exists (A083409(n)>1) for the given n.

Original entry on oeis.org

1369391, 87613571, 1172531, 216646267, 251331775687, 214159878489239, 750247439134737983

Offset: 2

Alexei Kourbatov and Hugo Pfoertner, May 11 2020

a(n) >= A210439(n). Equals A210439(n) at n=2,4,6, i.e., at those n for which there is only one type of prime n-tuplets (admissible prime n-tuples of minimal span). The corresponding minimal span (diameter) is given by A008407(n).
See A210439 for more information, references and links.
From Hugo Pfoertner, Oct 21 2021: (Start)
There are two options for choosing a(8):
Either one interprets "latest occurrence" as the largest number of 8-tuplets before the Hardy-Littlewood (H-L) prediction is exceeded, or one selects the larger value of the first 8-tuplet term causing the first crossing.
In the first case, 40634356 8-tuplets of the type p + [0, 2, 6, 12, 14, 20, 24, 26] are required before the H-L prediction is exceeded with an 8-tuplet 523250002674163757 + [0, 2, 6, ...].
In the second case, 20316822 8-tuplets of type p + [0, 6, 8, 14, 18, 20, 24, 26] are needed to reach the first crossing of the H-L prediction. The corresponding 8-tuplet has 750247439134737983 as first term.
The interchanging is a consequence of the different H-L constants for the two tuplet types, 475.36521.. vs. 178.261954.., which have a ratio of 8/3 to one another.
Since the H-L constant for the "earliest occurrence" A210439(8) is 178.26.., this speaks in favor of a choice from the two possibilities, which uses the same H-L constant, i.e., the occurrence with the larger tuplet start and not the occurrence with the larger number of required tuplets, for which a separate sequence A348053 is created. (End)

			Denote by pi_n(x) the n-tuplet counting function, C_n the corresponding Hardy-Littlewood constant, and Li_n(x) the integral from 2 to x of (1/(log t)^n) dt.
For 7-tuples with pattern (0 2 8 12 14 18 20) we have the Skewes number p=214159878489239; this is the initial prime p in the 7-tuple where for the first time we have pi_7(p) > C_7 Li_7(p). For the other dense pattern (0 2 6 8 12 18 20), the first sign change of pi_7(x) - C_7 Li_7(x) occurs earlier, at 7572964186421. Therefore we have a(7)=214159878489239, while A210439(7)=7572964186421.

Tony Forbes and Norman Luhn, Prime k-tuplets
Alexei Kourbatov, Optimized PARI code for computing a(7)
Norman Luhn, Database of the smallest prime k-tuplets, compressed files.
Hugo Pfoertner, Illustration of growth of number of 7-tuples, (2020).
Hugo Pfoertner, Comparison of number of octuplets needed to achieve the H-L prediction, (2021).

Cf. A008407, A083409, A210439, A333586, A333587, A348053.

PARI
```
See A. Kourbatov link.
```

\\ The first result is A210439(5), the 2nd is a(5)
Li(x, n)=intnum(t=2, n, 1/log(t)^x);
G5=(15^4/2^11)*0.409874885088236474478781212337955277896358; \\ A269843
n1=0;n2=0;n1found=0;n2found=0;p1=5;p2=7;p3=11;p4=13;
forprime(p5=17,10^12,if(p5-p1==12,my(L=Li(5,p1));if(p2-p1==2,n1++;if(!n1found&&n1/L>G5,print(p1," ",p2," ",n1," ",n1/L);n1found=1),n2++;if(!n2found&&n2/L>G5,print(p1," ",p2," ",n2," ",n2/L);n2found=1)));if(n1found&&n2found,break);p1=p2;p2=p3;p3=p4;p4=p5) \\ Hugo Pfoertner, May 12 2020
\\ Code for a(7), similar to A. Kourbatov's code but much shorter.
\\ Run time approx. 2 days, prints every 1000th 7-tuple
G7=(35^6/(3*2^22))*0.36943751038649868932319074987675; \\ A271742
s=[0,2,8,12,14,18,20];
r=[809, 2069, 2909, 5639, 6689, 7529, 7739, 8999, 10259, 12149, 12359, 14459, 14879, 15929, 17189, 19289, 20549, 21389, 23909, 24119, 26009, 27479, 28529, 28739];
forstep(p0=0,10^15,30030,for(j=1,24,my(p1=p0+r[j],isp=1,L);for(k=1,7,my(p=p1+s[k]);if(!ispseudoprime(p),isp=0;break));if(isp,L=Li(7,p1);n++;if(n%1000==0||n/L>G7,print(p1," ",p1+s[#s]," ",n/L," ",n));if(n/L>G7,break(2))))) \\ Hugo Pfoertner, May 16 2020

a(8) from Norman Luhn and Hugo Pfoertner, Oct 21 2021

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A210439 The minimal Skewes number for prime n-tuplets.

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A332493 The minimal Skewes number for prime n-tuplets, choosing the n-tuplet with latest occurrence of the first sign change relative to the Hardy-Littlewood prediction when more than one type of n-tuplets exists (A083409(n)>1) for the given n.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

PARI

PARI

Extensions