The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A269668 Smallest k >= 0 such that neither (k + 1)*n - k nor (k + 1)*n + k is prime. 2
 0, 2, 3, 0, 5, 0, 7, 0, 0, 0, 7, 0, 1, 0, 0, 0, 1, 0, 4, 0, 0, 0, 4, 0, 0, 0, 0, 0, 10, 0, 2, 0, 0, 0, 0, 0, 6, 0, 0, 0, 2, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 4, 0, 0, 0, 3, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that a(n) = m: 2, 31, 41, 131, 157, ... (for m = 2); 3, 53, 83, 97, 139, ... (for m = 3); 19, 23, 79, 191, ... (for m = 4), ... LINKS Antti Karttunen, Table of n, a(n) for n = 1..20000 EXAMPLE For n = 2, k = 0: (0 + 1)*2 - 0 = 2 is prime and (0 + 1)*2 + 0 = 2 is prime; for n = 2, k = 1: (1 + 1)*2 - 1 = 3 is prime and (1 + 1)*2 + 1 = 5 is prime; for n = 2, k = 2: (2 + 1)*2 - 2 = 4 is composite and (2 + 1)*2 + 2 = 6 is composite, so a(2) = 2. MATHEMATICA Table[SelectFirst[Range[0, 120], And[! PrimeQ[n (# + 1) - #], ! PrimeQ[n (# + 1) + #]] &], {n, 120}] (* Michael De Vlieger, Mar 04 2016, Version 10 *) PROG (PARI) A269668(n) = {my(k=0); while (isprime((k+1)*n-k) || isprime((k+1)*n+k), k++); k; } \\ Michel Marcus, Apr 04 2016, corrected by Antti Karttunen, Dec 27 2018 CROSSREFS Cf. A018252 (a(n) = 0), A068497 (a(n) = 1). Sequence in context: A145091 A085563 A071375 * A061397 A331045 A331044 Adjacent sequences: A269665 A269666 A269667 * A269669 A269670 A269671 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Mar 03 2016 EXTENSIONS Definition corrected by Michael De Vlieger, Mar 04 2016 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 June 15 10:19 EDT 2024. Contains 373407 sequences. (Running on oeis4.)