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A114231
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Smallest number m such that prime(n) + 2*prime(n-m) is a prime.
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6
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1, 1, 1, 3, 3, 1, 1, 1, 2, 1, 3, 2, 4, 4, 2, 9, 1, 3, 2, 4, 5, 1, 5, 2, 8, 3, 1, 3, 1, 1, 3, 8, 2, 6, 1, 4, 3, 8, 2, 7, 7, 14, 9, 7, 1, 4, 3, 1, 1, 1, 5, 1, 1, 2, 8, 4, 1, 8, 2, 4, 1, 8, 3, 9, 5, 3, 2, 1, 4, 1, 4, 4, 2, 3, 2, 4, 2, 12, 3, 1, 1, 3, 12, 2, 1, 2, 5, 5, 3, 3, 10, 4, 19, 1, 6, 4, 8, 7, 2, 5, 9, 2, 3
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OFFSET
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2,4
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LINKS
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EXAMPLE
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n=2, prime(2)+2*prime(2-1)=3+2*2=7 is prime, so a(2)=1;
n=3, prime(3)+2*prime(3-1)=5+2*3=11 is prime, so a(3)=1;
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n=17, prime(17)+2*prime(17-9)=59+2*19=97 is prime, so a(17)=9.
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MATHEMATICA
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Table[p1 = Prime[n1]; n2 = n1 - 1; p2 = Prime[n2]; While[cp = p1 + 2*p2; ! PrimeQ[cp], n2--; If[n2 == 0, Print[n1]]; p2 = Prime[n2]]; n1 - n2, {n1, 2, 201}]
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PROG
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(Haskell)
a114231 n = head [m | m <- [1..],
a010051 (a000040 n + 2 * a000040 (n - m)) == 1]
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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