login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A294639 a(n) = least prime p such that n divides p + prime(n). 1
2, 3, 7, 5, 19, 5, 11, 5, 13, 11, 2, 11, 11, 13, 13, 11, 43, 11, 47, 29, 11, 31, 101, 7, 3, 3, 5, 5, 7, 7, 59, 29, 61, 31, 61, 29, 139, 103, 67, 67, 67, 29, 67, 71, 73, 31, 71, 17, 67, 71, 73, 73, 607, 19, 73, 17, 73, 19, 313, 19, 83, 17, 71, 73, 337, 13, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence was inspired by A134204.

The logarithmic scatterplot of the sequence has interesting features (see Links section).

We observe runs of consecutive equal terms:

- first pair: a(12) = a(13) = 11,

- first triple: a(39) = a(40) = a(41) = 67,

- first quadruple: a(24980) = a(24981) = a(24982) = a(24983) = 12983.

a(1) = prime(1).

a(2) = prime(2).

LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..10000

Rémy Sigrist, Logarithmic scatterplot of the sequence for n=1..50000

Rémy Sigrist, Colored logarithmic scatterplot of the sequence for n=1..50000 (where the color is function of (a(n) + prime(n))/n)

EXAMPLE

For n=3:

- prime(3) = 5,

- 3 does not divide 2 + 5,

- 3 does not divide 3 + 5,

- 3 does not divide 5 + 5,

- 3 divides 7 + 5,

- hence a(3) = 7.

MAPLE

P:=proc(n) local k; k:=1; while ithprime(k)+ithprime(n) mod n>0 do

k:=k+1; od; ithprime(k); end: seq(P(i), i=1..10^2);

# Paolo P. Lava, Nov 17 2017

PROG

(PARI) a(n) = my (q=prime(n)); forprime(p=2, , if ((p+q)%n==0, return (p)))

CROSSREFS

Cf. A134204, A254862.

Sequence in context: A228775 A129543 A137440 * A038026 A051860 A155766

Adjacent sequences:  A294636 A294637 A294638 * A294640 A294641 A294642

KEYWORD

nonn,look

AUTHOR

Rémy Sigrist, Nov 05 2017

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 23 20:55 EDT 2019. Contains 325264 sequences. (Running on oeis4.)