

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
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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



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);


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



EXTENSIONS



STATUS

approved



