Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #19 Feb 24 2024 01:04:07
%S 111,2112,31113,411114,5111115,61111116,711111117,8111111118,
%T 91111111119,10111111111110,111111111111111,1211111111111112,
%U 13111111111111113,141111111111111114,1511111111111111115,16111111111111111116,171111111111111111117,1811111111111111111118
%N a(n) = n concatenated with n 1's and n.
%C All terms are divisible by 3. - Donald Sampson (marsquo(AT)hotmail.com), Dec 09 2003
%D J. Earls, On Smarandache Repunit N Numbers, Smarandache Notions Journal
%D (2004), Vol. 14.1, pp 251-258.
%F a(n) = n * 10^(n+L) + 10^L * R + n, where R is the n-th repunit and L is the number of decimal digits of n.
%t Array[FromDigits@ Join[#1, #2, #1] & @@ {IntegerDigits[#], ConstantArray[1, #]} &, 16] (* _Michael De Vlieger_, Mar 21 2018 *)
%Y Cf. A075842, A075858.
%K base,easy,nonn,less
%O 1,1
%A _Jason Earls_, Oct 15 2002
%E More terms from Donald Sampson (marsquo(AT)hotmail.com), Dec 09 2003