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 A066388 Numbers j such that j and 2j are both between a pair of twin primes. 12
 6, 30, 660, 810, 2130, 2550, 3330, 3390, 5850, 6270, 10530, 33180, 41610, 44130, 53550, 55440, 57330, 63840, 65100, 70380, 70980, 72270, 74100, 74760, 78780, 80670, 81930, 87540, 93240, 102300, 115470, 124770, 133980, 136950, 156420 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also terms of A014574 such that twice the term is also in A014574. Related to a problem of anti-divisors. A117499(a(n)) = 4. - Reinhard Zumkeller, Mar 23 2006 All a(n) > 6 must be a multiple of 30: As for elements of A014574, we must have a(n) = 6k, and k = 5m+-1 would lead to a(n)-+1 divisible by 5, while k = 5m+-2 would lead to 2*a(n)+-1 divisible by 5, so only k=5m is possible. - M. F. Hasler, Nov 27 2010 LINKS Harry J. Smith, Table of n, a(n) for n = 1..1000 Eric Weisstein's World of Mathematics, Bitwin Chain EXAMPLE For n=30, 29 and 31 are prime, as are 59 and 61. MATHEMATICA lst={}; Do[p1=Prime[n]; p2=Prime[n+1]; d=2; If[p2-p1==d, w=p1+1; If[PrimeQ[2*w-1]&&PrimeQ[2*w+1], AppendTo[lst, w]]], {n, 1, 10^4}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 07 2008 *) PROG (PARI) { n=0; forstep (m=2, 10^9, 2, if (isprime(m - 1) && isprime(m + 1) && isprime(2*m - 1) && isprime(2*m + 1), write("b066388.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Feb 13 2010 CROSSREFS Cf. A001359, A006512, A012574. Cf. A014574, A118859, A118860, A349321, A348348. Sequence in context: A349981 A075591 A130075 * A222718 A200894 A202861 Adjacent sequences: A066385 A066386 A066387 * A066389 A066390 A066391 KEYWORD nonn AUTHOR Jud McCranie, Dec 23 2001 STATUS approved

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Last modified September 21 06:04 EDT 2023. Contains 365486 sequences. (Running on oeis4.)