|
|
A259937
|
|
Concatenation of the numbers from 1 to n with numbers from n down to 1.
|
|
6
|
|
|
11, 1221, 123321, 12344321, 1234554321, 123456654321, 12345677654321, 1234567887654321, 123456789987654321, 1234567891010987654321, 12345678910111110987654321, 123456789101112121110987654321
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
For n < 700, only a(1) and a(10) are primes.
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
a(1) = 11.
a(5) = 1234554321.
|
|
MATHEMATICA
|
FromDigits /@ Flatten /@ IntegerDigits /@ (#~Join~Reverse@ # & /@ Table[Range@ n, {n, 12}]) (* Michael De Vlieger, Jul 10 2015 *)
|
|
PROG
|
(PARI) a(n)=my(r=""); for(i=0, n-1, r=concat(n-i, concat(r, n-i))); eval(r); \\ Anders Hellström, Aug 16 2015
(Python)
from itertools import chain
def A259937(n): return int(''.join(str(d) for d in chain(range(1, n+1), range(n, 0, -1)))) # Chai Wah Wu, Dec 20 2021
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|