|
|
A300517
|
|
a(n) is the concatenation of n n times, n-1 n-1 times, ..., 22, 1.
|
|
4
|
|
|
1, 221, 333221, 4444333221, 555554444333221, 666666555554444333221, 7777777666666555554444333221, 888888887777777666666555554444333221, 999999999888888887777777666666555554444333221, 10101010101010101010999999999888888887777777666666555554444333221
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
a(n) is composite for all 2 <= n <= 1000. - David Cleaver, Apr 14 2023
|
|
LINKS
|
|
|
EXAMPLE
|
a(4) = 4444333221 because 4 concatenated four times then concatenated with 3 three times and 2 twice and 1 once gives 4444333221.
|
|
MAPLE
|
a:= n-> parse(cat(seq((n-i)$(n-i), i=0..n-1))):
|
|
PROG
|
(Ruby)
a = '1'
[1] + (2..n).map{|i| a = (i.to_s * i + a.to_s).to_i}
end
(PARI)
a(n) = {my(a=0, b=0, d=1, i);
for(i=1, n, b = logint(i, 10)+1;
a += d*i*(10^(i*b)-1)/(10^b-1);
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|