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未解決問題解説
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Proof of Cramér's conjecture

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When we write log, we refer to natural logarithm. Let n be an integer, x be a real number and pn be the nth prime. Let f(x)=(logx)2logx. f(x)<0 holds for x>e3/2=4.4816 since f(x)=(2logx1)/x and f(x)=(32logx)/x2 hold. Therefore, the following inequality holds for n3 where pn5 holds.
(2logpn+11)/pn+1<((logpn+1)2logpn+1((logpn)2logpn))/(pn+1pn)
pn+1pn<((logpn+1)2(logpn)2logpn+1+logpn)pn+1/(2logpn+11) (1)
We consider the following inequality.
((logpn+1)2logpn+11(logpn)2+logpn+1)pn+1/(2logpn+11)
<(logpn)2logpn1 (2)
((logpn+1)2logpn+11)/((logpn)2logpn1)<(2logpn+11)/pn+1+1
In the meantime,
((logpn+1)2logpn+11)/((logpn)2logpn1)(logpn+1)2/(logpn)2<(1+1/n)2
((logpn+1)2logpn+11)/((logpn)2logpn1)<(1+1/n)2 (3)
holds by Firoozbakht's conjecture logpn+1/logpn<1+1/n holds for n1. And the inequality (3) holds for n7. If the following inequality holds, then the inequality (2) holds.
(1+1/n)2<(2logpn+11)/pn+1+1
(2n+1)pn+1<(2logpn+11)n2 (4)
Let O be the big O notation. This inequality holds for greater than a certain value since pnnlogn holds and the divergence speed of the right-hand side O(n2log(nlogn)) is greater than the one of the left-hand side O(n2logn). Let a(n) be as follows.
a(n)=(2logpn+11)n2(2n+1)pn+1
a(24)=58.93295276410298892153669179703610
a(25)=7.09935394842568639475216635876355
a(26)=131.15359208646756207915032995225198
a(27)=198.98444064545920067781347521993786
a(28)=359.03347933529732219163219706402818
It is confirmed that a(n)>0 holds for n26 and the inequalities (2) and (4) hold for n26. Let b(n) be as follows.
b(n)=(2logpn+11)/pn+1+1(((logpn+1)2logpn+11)/((logpn)2logpn1))
b(1)=0.66380016877133500169596535659586
b(2)=1.42230123209370924210334867419603
b(3)=45.31730044379500592507223531774951
b(4)=1.45275033447687539540881968563566
b(5)=0.03621871624815341884765243475238
b(6)=0.11696498127210133687103450742783
b(7)=0.13060167724403583947233671682271
b(8)=0.02377871508265959623651270293433
b(9)=0.02620098992667876420188430014817
b(10)=0.13379184221862893822797750407684
b(11)=0.02280728849612000349535364370096
b(12)=0.07972475475815013500604912501867
b(13)=0.11771003199119562213027762878889
b(14)=0.07990246073882603960262344914834
b(15)=0.04879289184018860944723712043827
b(16)=0.05124064046859100815357775875139
b(17)=0.09763940776440667306019287224712
b(18)=0.05236647301446298167470997077398
b(19)=0.07127986254758770005483568368378
b(20)=0.08759263975507364608996390701565
b(21)=0.05183605561149361606563646315404
b(22)=0.06639699381302652671846163803069
b(23)=0.05051012684827756106675916967605
b(24)=0.03666906632945060472824881557505
b(25)=0.05993204099042169573922376487906
It is confirmed that b(n)>0 holds for 10n25 and the inequality (2) holds for n10. Let c(n)=(logpn)2logpn(pn+1pn).
c(1)=1.21269416664174388475012959513151
c(2)=1.89166332785552771355146611307315
c(3)=1.01914751845386542942058832823353
c(4)=2.15934384085884166054381434633934
c(5)=1.35200646651040134639585630912732
c(6)=0.01401584888081342190407137886266
c(7)=3.19388450888199055317433828810166
c(8)=1.72528192286826953728521711950189
c(9)=0.69582976219600349584379069026756
It is confirmed that c(n)>0 holds for n5. From the above, it is proved that pn+1pn<(logpn)2logpn1 holds for n10 by the inequalities (1) and (2) and pn+1pn<(logpn)2logpn holds for n5. (Q.E.D.)

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