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

17, 214, 321, 428, 535, 642, 749, 856, 963, 1070, 1177, 1284, 1391, 1498, 15105, 16112, 17119, 18126, 19133, 20140, 21147, 22154, 23161, 24168, 25175, 26182, 27189, 28196, 29203, 30210, 31217, 32224, 33231, 34238, 35245, 36252, 37259, 38266, 39273, 40280

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base
• less
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

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).

Programs

Magma

[Seqint(Intseq(7*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014

Mathematica

nxt[n_]:=Module[{idn=IntegerDigits[n], idn7=IntegerDigits[7n]}, FromDigits[Join[idn, idn7]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *)
Table[n*10^IntegerLength[7n]+7n,{n,40}] (* Harvey P. Dale, Aug 02 2024 *)