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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
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
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
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