A156053 Let m = A002445(n); then a(n) = largest member of A001359 (the lesser twin primes sequence) <= m.

5, 29, 41, 2729, 137, 14321, 281, 3404309, 33329, 641, 4206929, 1366529, 281189, 7589, 625169, 5009, 2081, 63029, 5477, 2657, 2801, 15269, 19469, 25997, 49169, 11489, 23909, 289109, 14009, 129629, 32909, 3254729, 88577309, 93809, 412589

Offset: 1

Author

Bill McEachen, Feb 02 2009

Keywords

• easy
• nonn

Links

• Wikimedia Commons, Alternate plot

Crossrefs

Cf. A002445

Programs

PARI

\\ uses Pari functions ispseudoprime, denominator, and list \\ tp2cnt =count of adjacent, unique twin primes (lower) \\ p2cnt = count of unique adjacent primes \\ N = Bernoulli # maxx= max N idx*=list pointers \\ u=array of adj. unique TP u2=array of adj. unique primes cnt=0;pcnt=0;n=1;opcnt=0;plcnt=0;phcnt=0;tpcnt=0;otpcnt=0; tp2cnt=0;p2cnt=0; limmit=429000001; \\4E8 idx=1; \\init idx2=1;
\\init if(maxx<2,maxx=2); if(maxx>200000,maxx=200000); print ("enforced n max = ",maxx); u=listcreate(500); \\unique entries < 10% TP u2=listcreate(5000); \\unique entries < 50% while(notpcnt, print("TP! @ ",n," ",q, " "
\\IF.FOR,IF if(p>0,listput(u,p,idx);tp2cnt++ ); if(p>0,idx++) ); \\ end IF if( pcnt>opcnt, if(p>limmit,p=0); \\lower if(ispseudoprime(p)==0,p=0); if(p>0, for(z=1,idx2-1, if(p==u2[z],p=0); ); ); if(p>0,listput(u2,p,idx2);p2cnt++); if(p>0,idx2++); if(q>limmit,q=0);
\\upper if(ispseudoprime(q)==0,q=0); if(q>0, for(z=1,idx2-1, if(q==u2[z],q=0); ); ); if(q>0,listput(u2,q,idx2);p2cnt++); if(q>0,idx2++) ); \\ end IF opcnt=pcnt;otpcnt=tpcnt; n++ ); \\end WHILE if(cnt>0, print(2.*p2cnt/cnt) ); \\reflect every other (n.z.) print ("TP count = ",tp2cnt ); print ("enforced n max = ",maxx);

Extensions

Edited by N. J. A. Sloane, Oct 21 2009