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A248511
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Difference between k and the least prime factor of k^2+1 where k is the n-th number with k^2+1 composite.
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1
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1, 3, 5, 3, 7, 9, 7, 11, 13, 15, 13, 17, 19, 17, 21, 23, 25, 23, 27, 13, 29, 27, 31, 21, 33, 35, 33, 37, 39, 37, 41, 31, 43, 17, 45, 43, 47, 9, 49, 47, 51, 53, 55, 53, 57, 47, 59, 57, 61, 47, 63, 65, 63, 67, 57, 69, 67, 71, 73, 23, 75, 73, 77, 43, 79, 77, 81
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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a(1) = 1 because the first composite is 3^2+1 = 2*5 and 3-2 = 1.
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MAPLE
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with(numtheory):
for n from 1 to 200 do:
p:=n^2+1:x:=factorset(p):d:=n-x[1]:
if type(p, prime)=false
then
printf(`%d, `, d):
else
fi:
od:
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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