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 A056140 a(n) = n^2 - previousprime(n)*nextprime(n), for n>2. 2
 -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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,3 COMMENTS a(n) is never 0. LINKS FORMULA a(n) = n^2-A007917(n-1)*A007918(n+1) = A000290(n)-A013638(n). EXAMPLE a(3)=3^2-2*5=-1, a(4)=4^2-3*5=1. MATHEMATICA Table[n^2-NextPrime[n]NextPrime[n, -1], {n, 3, 80}] (* Harvey P. Dale, Aug 22 2011 *) PROG (PARI) a(n) = n^2 - precprime(n-1)*nextprime(n+1); \\ Michel Marcus, Mar 22 2020 CROSSREFS Cf. A056139, A056141. Sequence in context: A083843 A094264 A298829 * A225419 A140895 A191714 Adjacent sequences:  A056137 A056138 A056139 * A056141 A056142 A056143 KEYWORD easy,sign AUTHOR Henry Bottomley, Jun 15 2000 EXTENSIONS More terms from Harvey P. Dale, Aug 22 2011 STATUS approved

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Last modified April 11 11:31 EDT 2021. Contains 342886 sequences. (Running on oeis4.)