Search: id:A135283
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%I A135283
%S A135283 13,23,41,65,101,143,191,245,311,353,425,479,551,581,623,695,749,821,
%T A135283 875,971,1115,1271,1325,1445,1613,1739,1817,1877,1943,2129,2441,2471,
%U A135283 2513,2597,2783,3071,3113,3161,3215,3335,3533,3737,3845,3881,3923,4067
%N A135283 Sum of staircase twin primes according to the rule: top + bottom + next 
               top.
%C A135283 We list the twin primes in staircase fashion as follows.
%C A135283 3
%C A135283 5_5
%C A135283 __7_11
%C A135283 ____13_17
%C A135283 _______19_29
%C A135283 __________31_41
%C A135283 _____________.._..
%C A135283 ________________tu(n)_tl(n)
%C A135283 ______________________tu(n+1)
%C A135283 ...
%C A135283 where tl(n) = n-th lower twin prime, tu(n) = n-th upper twin prime. Then 
               a(n) = tl(n) + tu(n) + tl(n+1).
%o A135283 (PARI) g(n) = for(x=1,n,y=twinu(x)+twinl(x) + twinl(x+1);print1(y",")) 
               twinl(n) = / *The nth lower twin prime. */ { local(c,x); c=0; x=1; 
               while(c<n, if(ispseudoprime(prime(x)+2),c++); x++; ); return(prime(x-1)) 
               } twinu(n) = /* The nth upper twin prime. */ { local(c,x); c=0; x=1; 
               while(c<n, if(isprime(prime(x)+2),c++); x++; ); return(prime(x)) 
               }
%Y A135283 Sequence in context: A164434 A164494 A164407 this_sequence A119488 A165350 
               A112394
%Y A135283 Adjacent sequences: A135280 A135281 A135282 this_sequence A135284 A135285 
               A135286
%K A135283 nonn
%O A135283 1,1
%A A135283 Cino Hilliard (hillcino368(AT)hotmail.com), Dec 02 2007

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