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A056140
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a(n) = n^2 - previousprime(n)*nextprime(n), for n>2.
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2
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-1, 1, 4, 1, -6, -13, 4, 23, 30, 1, -18, -25, 4, 35, 42, 1, -30, -37, 4, 47, -22, -91, -42, 9, 62, 117, 128, 1, -112, -123, -58, 9, 78, 149, 98, -73, 4, 83, 90, 1, -78, -85, 4, 95, -70, -187, -90, 9, 110, 213, 36, -211, -102, 9, 122, 237, 248, 1, -232, -243
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OFFSET
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3,3
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COMMENTS
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a(n) is never 0.
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LINKS
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FORMULA
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EXAMPLE
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a(3)=3^2-2*5=-1, a(4)=4^2-3*5=1.
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MATHEMATICA
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Table[n^2-NextPrime[n]NextPrime[n, -1], {n, 3, 80}] (* Harvey P. Dale, Aug 22 2011 *)
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PROG
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(PARI) a(n) = n^2 - precprime(n-1)*nextprime(n+1); \\ Michel Marcus, Mar 22 2020
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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