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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
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, 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.
PROG
(PARI) a(n) = my (q=prime(n)); forprime(p=2, , if ((p+q)%n==0, return (p)))
CROSSREFS
Sequence in context: A228775 A129543 A137440 * A038026 A051860 A351494
KEYWORD
nonn,look
AUTHOR
Rémy Sigrist, Nov 05 2017
STATUS
approved