A018866 7^a(n) is smallest power of 7 beginning with n.

0, 4, 3, 2, 8, 14, 1, 7, 13, 45, 6, 38, 12, 57, 31, 5, 50, 37, 11, 69, 43, 30, 17, 4, 49, 36, 23, 10, 68, 55, 42, 29, 16, 3, 61, 48, 35, 106, 22, 9, 67, 138, 54, 41, 28, 99, 15, 228, 2, 60, 131, 47, 260, 34, 21, 92, 8, 150, 66, 137, 53, 195, 40, 182, 27, 98, 14, 85, 298, 72, 285

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Links

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

Programs

Mathematica

With[{s=7^Range[0,500]},Flatten[Table[Position[s,?(IntegerDigits[n] ==  Take[IntegerDigits[#],IntegerLength[n]]&),1,1],{n,80}]]]-1//Quiet (* _Harvey P. Dale, Feb 22 2018 *)