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 A158866 Indices of twin primes if the sum of these twin primes+1 is an upper twin prime. 3
 2, 5, 30, 31, 66, 73, 88, 91, 141, 147, 217, 513, 607, 637, 743, 760, 784, 845, 856, 911, 920, 938, 949, 958, 994, 1015, 1031, 1092, 1150, 1246, 1373, 1470, 1553, 1586, 1768, 1814, 1871, 2017, 2029, 2129, 2261, 2271, 2331, 2370, 2458, 2488, 2510, 2545, 2579 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If the sum is a member of a twin prime pair, it always is the upper twin prime member. [Proof: Twin primes are sequentially of the form 6n-1 and 6n+1. Then adding according to the condition, we get 6n-1+6n+1+1 = 12n+1. This implies 12n+1 is an upper member since if it were a lower member, 12n+1+2 would be the upper member but 12n+3 is not prime contradicting the definition of a twin prime. Therefore 12n+1 must be an upper twin prime member as stated.] LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA {k: A054735(k)+1 = A006512(j), any j} - R. J. Mathar, Apr 06 2009 EXAMPLE The 30th lower twin prime is 659. 659+661+1 = 1321, prime and 1319 is too. Then 1319 is the lower member of the twin prime pair (1319,1321). So 30 is in the sequence. MAPLE count:= 0: Res:= NULL: k:= 1: for j from 1 while count < 100 do   if isprime(6*j-1) and isprime(6*j+1) then     k:= k+1;     if isprime(12*j-1) and isprime(12*j+1) then        count:= count+1;        Res:= Res, k;     fi   fi od: Res; # Robert Israel, Mar 06 2018 MATHEMATICA utpQ[{a_, b_}]:=And@@PrimeQ[a + b + {1, -1}]; Flatten[Position[Select[ Partition[Prime[Range], 2, 1], #[]-#[]==2&], _?utpQ]] (* Harvey P. Dale, Sep 16 2013 *) PROG (PARI) twinl(n) = { local(c, x); c=0; x=1; while(c

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Last modified June 16 14:41 EDT 2021. Contains 345057 sequences. (Running on oeis4.)