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A346150
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Alternating runs of primes and composites, with the runs of primes being of composite length and the runs of composites being of prime length.
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0
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2, 4, 6, 3, 5, 7, 11, 8, 9, 10, 13, 17, 19, 23, 29, 31, 12, 14, 15, 16, 18, 37, 41, 43, 47, 53, 59, 61, 67, 20, 21, 22, 24, 25, 26, 27, 71, 73, 79, 83, 89, 97, 101, 103, 107, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42
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OFFSET
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1,1
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COMMENTS
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In other words, use sequence A073846 to list alternating runs of primes and composites, with the number of elements in each run given by successive terms in A073846 - with each even-indexed term of A073846 (being itself prime) denoting the length of each run of composites and each odd-indexed term of A073846 (being itself composite) denoting the length of each run of primes.
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LINKS
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EXAMPLE
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a(1) = 2, this being a length 1 (1 is initial index) run of primes.
a(2) = 4 & a(3) = 6, 4 and 6 being a length 2 (2 is first prime) run of composites.
a(4) = 3, a(5) = 5, a(6) = 7, and a(7) = 11 being a length 4 (4 is first composite) run of primes.
a(8) = 8, a(9) = 9, and a(10) = 10, being a length 3 (3 is 2nd prime) run of composites.
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MATHEMATICA
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m=10; c1=Select[Range@m, !PrimeQ@#&]; p1=Prime@Range@Total@c1; p2=Prime@Range@m; c2=Select[Range[2, 2Total@p2], !PrimeQ@#&][[;; Total@p2]]; t1=TakeList[p1, c1]; t2=TakeList[c2, p2]; min=Min[Length/@{t1, t2}]; Flatten@Riffle[t1[[;; min]], t2[[;; min]]] (* Giorgos Kalogeropoulos, Jul 30 2021 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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