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A306878 Number of 0 < k < n such that n-k and n+k are both nonprimes. 0
0, 0, 0, 0, 2, 1, 2, 3, 3, 3, 5, 5, 6, 6, 7, 6, 9, 10, 8, 10, 11, 10, 12, 13, 13, 13, 15, 14, 16, 18, 15, 18, 20, 16, 20, 21, 20, 21, 24, 21, 23, 26, 24, 24, 29, 25, 27, 30, 26, 30, 32, 29, 31, 33, 31, 33, 36, 33, 34, 41, 34, 36, 42, 35, 40, 42, 40, 40, 43, 42, 44, 48, 44, 44 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..74.

FORMULA

a(n) = n - 1 - A061357(n) - A291564(n).

PROG

(PARI) a(n)=my(s); for(c=1, n-1, s+=(bigomega(n-c)-1)*(bigomega(n+c)-1)!=0); s

CROSSREFS

Cf. A061357, A291564.

Sequence in context: A008681 A097242 A183202 * A161308 A161242 A161027

Adjacent sequences:  A306875 A306876 A306877 * A306879 A306880 A306881

KEYWORD

nonn

AUTHOR

Gionata Neri, Mar 14 2019

STATUS

approved

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Last modified February 26 16:33 EST 2020. Contains 332284 sequences. (Running on oeis4.)