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A009441 a(n) is the concatenation of n and 7n. 9

%I

%S 17,214,321,428,535,642,749,856,963,1070,1177,1284,1391,1498,15105,

%T 16112,17119,18126,19133,20140,21147,22154,23161,24168,25175,26182,

%U 27189,28196,29203,30210,31217,32224,33231,34238,35245,36252,37259,38266,39273,40280

%N a(n) is the concatenation of n and 7n.

%H Vincenzo Librandi, <a href="/A009441/b009441.txt">Table of n, a(n) for n = 1..1000</a>

%t nxt[n_]:=Module[{idn=IntegerDigits[n], idn7=IntegerDigits[7n]}, FromDigits[Join[idn, idn7]]]; Array[nxt, 100] (* _Vincenzo Librandi_, Feb 04 2014 *)

%o (MAGMA) [Seqint(Intseq(7*n) cat Intseq(n)): n in [1..50]]; // _Vincenzo Librandi_, Feb 04 2014

%Y Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), A019551 (k=3), A019552 (k=4), A019553 (k=5), A009440 (k=6), this sequence (k=7), A009470 (k=8), A009474 (k=9).

%K nonn,base,less,easy

%O 1,1

%A _David W. Wilson_

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Last modified October 14 00:31 EDT 2019. Contains 327991 sequences. (Running on oeis4.)