The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A120225 a(n) is the minimal number k>n such that n+k and n*k+1 are primes. 6
 2, 3, 4, 7, 6, 7, 10, 9, 14, 13, 18, 19, 24, 15, 16, 21, 24, 29, 22, 21, 22, 31, 30, 43, 28, 33, 34, 39, 32, 41, 36, 39, 34, 37, 66, 43, 60, 41, 50, 43, 42, 55, 46, 53, 52, 51, 50, 59, 52, 51, 56, 55, 56, 55, 58, 75, 74, 69, 68, 67, 66, 75, 74, 67, 86, 83, 70, 89, 70, 79, 102, 79 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Differs from A120224 in the first term. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE a(3)=4 because 3+4=7 and 3*4+1=13 are prime; a(8)=9 because 8+9=17 and 8*9+1=73 are prime, MATHEMATICA Reap[Do[Do[If[PrimeQ[{n+x, n*x+1}]=={True, True}, Sow[x]; Break[]], {x, n+1, 1000}], {n, 120}]][[2, 1]] mnk[n_]:=Module[{k=n+1}, While[!AllTrue[{n+k, n*k+1}, PrimeQ], k++]; k]; Array[ mnk, 80] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 15 2015 *) CROSSREFS Cf. A085063, A092945, A085063, A120223, A120224. Sequence in context: A319651 A340632 A074846 * A247798 A130685 A210202 Adjacent sequences:  A120222 A120223 A120224 * A120226 A120227 A120228 KEYWORD nonn AUTHOR Zak Seidov, Jun 10 2006 STATUS approved

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

Last modified November 30 08:19 EST 2021. Contains 349419 sequences. (Running on oeis4.)