A259937 Concatenation of the numbers from 1 to n with numbers from n down to 1.
11, 1221, 123321, 12344321, 1234554321, 123456654321, 12345677654321, 1234567887654321, 123456789987654321, 1234567891010987654321, 12345678910111110987654321, 123456789101112121110987654321
Offset: 1
Examples
a(1) = 11. a(5) = 1234554321.
Programs
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Mathematica
FromDigits /@ Flatten /@ IntegerDigits /@ (#~Join~Reverse@ # & /@ Table[Range@ n, {n, 12}]) (* Michael De Vlieger, Jul 10 2015 *) -
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
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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
Comments