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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
OFFSET
3,3
COMMENTS
a(n) is never 0.
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
Sequence in context: A083843 A094264 A298829 * A225419 A140895 A343599
KEYWORD
easy,sign
AUTHOR
Henry Bottomley, Jun 15 2000
EXTENSIONS
More terms from Harvey P. Dale, Aug 22 2011
STATUS
approved