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%I #36 Dec 30 2023 23:43:23
%S 14,28,312,416,520,624,728,832,936,1040,1144,1248,1352,1456,1560,1664,
%T 1768,1872,1976,2080,2184,2288,2392,2496,25100,26104,27108,28112,
%U 29116,30120,31124,32128,33132,34136,35140,36144,37148,38152,39156,40160,41164
%N a(n) is the concatenation of n and 4n.
%C a(n) is divisible by 4 for n >= 2. - _Michel Marcus_, Sep 21 2015
%H Vincenzo Librandi, <a href="/A019552/b019552.txt">Table of n, a(n) for n = 1..1000</a>
%H Sylvester Smith, <a href="https://www.gallup.unm.edu/~smarandache/SYLSMITH.HTM">A Set of Conjectures on Smarandache Sequences</a>, Bulletin of Pure and Applied Sciences, (Bombay, India), Vol. 15 E (No. 1), 1996, pp. 101-107.
%p a:=n->n*10^floor(log10(4*n)+1)+4*n: seq(a(n),n=1..50); # _Muniru A Asiru_, Jun 23 2018
%t Table[FromDigits[Join[IntegerDigits[n],IntegerDigits[4n]]],{n,50}] (* _Harvey P. Dale_, May 11 2011 *)
%t nxt[n_]:=Module[{idn=IntegerDigits[n], idn4=IntegerDigits[4n]}, FromDigits[Join[idn, idn4]]]; Array[nxt, 100] (* _Vincenzo Librandi_, Feb 04 2014 *)
%o (Magma) [Seqint(Intseq(4*n) cat Intseq(n)): n in [1..50]]; // _Vincenzo Librandi_, Feb 04 2014
%o (PARI) a(n) = eval(Str(n, 4*n)); \\ _Michel Marcus_, Sep 21 2015
%Y Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), A019551 (k=3), this sequence (k=4), A019553 (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9).
%K nonn,base,less,easy
%O 1,1
%A R. Muller
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