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 A009440 a(n) is the concatenation of n and 6n. 9
 16, 212, 318, 424, 530, 636, 742, 848, 954, 1060, 1166, 1272, 1378, 1484, 1590, 1696, 17102, 18108, 19114, 20120, 21126, 22132, 23138, 24144, 25150, 26156, 27162, 28168, 29174, 30180, 31186, 32192, 33198, 34204, 35210, 36216, 37222, 38228, 39234, 40240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 MATHEMATICA nxt[n_]:=Module[{idn=IntegerDigits[n], idn6=IntegerDigits[6n]}, FromDigits[Join[idn, idn6]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *) Table[n*10^IntegerLength[6n]+6n, {n, 40}] (* Harvey P. Dale, Jul 21 2020 *) PROG (MAGMA) [Seqint(Intseq(6*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014 CROSSREFS Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), A019551 (k=3), A019552 (k=4), A019553 (k=5), this sequence (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9). Sequence in context: A319236 A222447 A059385 * A284226 A282395 A273588 Adjacent sequences:  A009437 A009438 A009439 * A009441 A009442 A009443 KEYWORD nonn,base,less,easy AUTHOR STATUS approved

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Last modified September 18 19:19 EDT 2020. Contains 337172 sequences. (Running on oeis4.)