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A102484
Numbers of the concatenated form 9nn9.
5
9009, 9119, 9229, 9339, 9449, 9559, 9669, 9779, 9889, 9999, 910109, 911119, 912129, 913139, 914149, 915159, 916169, 917179, 918189, 919199, 920209, 921219, 922229, 923239, 924249, 925259, 926269, 927279, 928289, 929299, 930309
OFFSET
1,1
LINKS
FORMULA
a(n) = 9*(1 + 10^(2*A055642(n-1)+1))+(n-1)*(10+10^(1+A055642(n-1))). - Robert Israel, May 09 2017
EXAMPLE
For n=0 we concatenate 3, 0, 0 and 3 to get 3003.
For n=10 we concatenate 3, 10, 10 and 3 to get 310103.
MAPLE
f:= n -> 9 + 9*10^(2*ilog10(n-1)+3)+(n-1)*(10+10^(2+ilog10(n-1))):
f(1):= 9009;
map(f, [$1..200]); # Robert Israel, May 09 2017
MATHEMATICA
With[{k = {9}}, Table[FromDigits@ Join[k, #, #, k] &@ IntegerDigits[n], {n, 0, 30}]] (* Michael De Vlieger, May 09 2017 *)
CROSSREFS
Cf. A100846 for 1nn1; A100896 for 3nn3; A100897 for 7nn7.
Cf. A055642.
Sequence in context: A202531 A106770 A326319 * A295457 A359845 A252456
KEYWORD
easy,nonn,base
AUTHOR
Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 12 2005
STATUS
approved