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A085417
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Take prime[n] and continue adding n,n+1,..., n+a(n)-1 until one reaches a prime.
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4
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1, 1, 3, 1, 3, 1, 3, 9, 3, 5, 3, 5, 3, 12, 4, 9, 3, 1, 3, 4, 3, 1, 4, 1, 7, 1, 7, 5, 3, 4, 3, 1, 3, 1, 3, 8, 3, 9, 7, 5, 4, 1, 8, 12, 4, 4, 15, 1, 8, 21, 3, 5, 24, 9, 12, 8, 3, 4, 3, 9, 11, 4, 3, 5, 48, 1, 7, 33, 3, 1, 3, 1, 15, 12, 3, 5, 8, 5, 3, 36, 19, 1, 3, 5, 11, 5, 12, 5, 4, 4, 3, 1, 3, 5, 3, 1, 15, 1
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OFFSET
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1,3
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COMMENTS
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LINKS
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EXAMPLE
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a(3)=3 because prime[3]=5 and 5+(3+4+5)=17= is a prime A085418(3).
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MAPLE
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f:= proc(n) local m, k, x;
m:= ithprime(n) - (n-1)*n/2;
for k from n do
x:= k*(k+1)/2 + m;
if isprime(x) then return k+1-n fi
od;
end proc:
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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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STATUS
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approved
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