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 A087382 Twin prime indices of primes forming a twin prime member. 0
 3, 5, 7, 11, 13, 17, 29, 41, 43, 61, 109, 149, 179, 191, 269, 313, 347, 431, 461, 463, 601, 617, 643, 659, 829, 859, 1031, 1033, 1051, 1231, 1279, 1321, 1619, 1621, 1879, 1931, 1949, 1999, 2029, 2309, 2311, 2341, 2383, 2711, 2789, 2791, 2801, 3253, 3299, 3329 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 COMMENTS It is interesting that these primes occur rather frequently early on but gradually diminish as the iterations increase. Some ratios of count of twin primes p and the occurrence of prime(p) also a twin prime is as follows. Index< Ratio 1000 .74 10000 .48 100000 .39 1000000 .35 Looks like it is approaching a limit. LINKS Table of n, a(n) for n=3..52. EXAMPLE The 29th prime,109,is also a twin prime paired with the prime 107. PROG (PARI) twips(n) = { c1=0; c2=0; forprime(x=3, n, if(isprime(x+2), c1++); x1=prime(x); if(isprime(x-2) || isprime(x+2), if(isprime(x1-2) || isprime(x1+2), print1(x", "); c2++; ) ) ); print(); print(c2/c1+.0) } CROSSREFS Sequence in context: A088503 A118939 A239391 * A355845 A025127 A024883 Adjacent sequences: A087379 A087380 A087381 * A087383 A087384 A087385 KEYWORD easy,nonn AUTHOR Cino Hilliard, Oct 21 2003 STATUS approved

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Last modified December 1 23:26 EST 2023. Contains 367503 sequences. (Running on oeis4.)