A180728 21^a(n) is smallest power of 21 beginning with n.

0, 1, 8, 2, 21, 15, 9, 6, 3, 28, 25, 22, 19, 16, 13, 10, 38, 7, 4, 32, 1, 29, 26, 85, 23, 82, 20, 79, 48, 17, 45, 14, 73, 42, 11, 39, 8, 67, 36, 5, 64, 33, 362, 2, 61, 30, 89, 58, 387, 27, 86, 55, 384, 24, 83, 52, 1191, 21, 80, 1219, 49, 288, 18, 77, 946, 46, 285, 15, 74, 1483, 43

Offset: 1

Author

Daniel Mondot, Sep 18 2010

Keywords

• base
• nonn

Links

• D. Mondot, Table of n, a(n) for n=1..32699

Crossrefs

Cf. A180726, A180727, A180730

Programs

Mathematica

Module[{nn=1500,t21},t21=Table[{n,IntegerDigits[21^n]},{n,0,nn}];Table[SelectFirst[ t21,IntegerDigits[k]==Take[#[[2]],IntegerLength[k]]&],{k,80}]][[;;,1]]//Quiet (* Harvey P. Dale, May 14 2023 *)