The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 16 20:11 EDT 2022. Contains 353720 sequences. (Running on oeis4.)