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 A075570 Lexicographically earliest sequence of distinct composite numbers such that a(k) + a(k+1) is prime for all k. 5
 4, 9, 8, 15, 14, 27, 10, 21, 16, 25, 6, 35, 12, 49, 18, 55, 24, 65, 32, 39, 20, 33, 26, 45, 22, 51, 28, 69, 34, 63, 38, 75, 52, 57, 40, 87, 44, 93, 46, 81, 50, 77, 30, 119, 48, 91, 36, 95, 42, 85, 54, 125, 56, 111, 62, 105, 58, 99, 64, 115, 66, 133, 60, 121, 70, 123, 68, 129, 82 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Index of composite values: {1, 4, 3, 8, 7, 17, 5, 12, 9, 15, 2, 23, 6, 33, 10, 38, 14, 46, 20, 26, 11, 21, 16, 30, ...}. - Michael De Vlieger, Jul 18 2017 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..3000 MAPLE P:=proc(q) local a, k, n; a:=[1]: for k from 1 to 65 do for n from 1 to q do if not isprime(n) and numboccur(a, n)=0 and isprime(n+a[nops(a)]) then a:=[op(a), n]; break; fi; od; od; a:=subsop(1=NULL, a); end: P(10^3); # Paolo P. Lava, Jun 05 2019 MATHEMATICA a = {4}; Do[k = 2 - Boole@ EvenQ@ n; While[Nand[! MemberQ[a, k], CompositeQ@ k, PrimeQ[a[[n - 1]] + k]], k += 2]; AppendTo[a, k], {n, 2, 69}]; a (* Michael De Vlieger, Jul 18 2017 *) CROSSREFS Cf. A025044, A072525, A085084, A240024. Sequence in context: A357313 A085084 A248390 * A308289 A236630 A351381 Adjacent sequences: A075567 A075568 A075569 * A075571 A075572 A075573 KEYWORD nonn AUTHOR Amarnath Murthy, Sep 25 2002 EXTENSIONS More terms from David Wasserman, Jan 20 2005 Definition clarified by Peter Munn, Jul 20 2017 STATUS approved

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Last modified September 26 08:38 EDT 2023. Contains 365654 sequences. (Running on oeis4.)