A168541 Numbers consisting of either 2's and 0's or 5's and 0's.

2, 5, 20, 50, 200, 202, 220, 500, 505, 550, 2000, 2002, 2020, 2022, 2200, 2202, 2220, 5000, 5005, 5050, 5055, 5500, 5505, 5550, 20000, 20002, 20020, 20022, 20200, 20202, 20220, 20222, 22000, 22002, 22020, 22022, 22200, 22202, 22220, 50000, 50005

Offset: 1

Author

David Applegate, Marc LeBrun and N. J. A. Sloane, Jul 06 2010

Keywords

• nonn
• base
• easy

Comments

A subset of the divisors of zero in carryless arithmetic mod 10, e.g., 5 * 44 = 0.

Links

• David Applegate, Marc LeBrun and N. J. A. Sloane, Carryless Arithmetic (I): The Mod 10 Version.
• Index entries for 10-automatic sequences.
• Index entries for sequences related to carryless arithmetic

Crossrefs

Cf. A004520, A059729, A168294, A169884.

Programs

Mathematica

lst = {2, 5}; k = 1; While[k < 10^5, id = Union@ IntegerDigits@k; len = Length@ id; If[ len == 2 && id == {0, 2} || id == {0, 5}, AppendTo[lst, k]]; k++ ]; lst (* Robert G. Wilson v, Jul 12 2010 *)
Join[{2,5},Sort[Flatten[Table[Select[FromDigits/@Tuples[{k,0},6],DigitCount[ #,10,0]>0 && DigitCount[#,10,k]>0&],{k,{2,5}}]]]] (* Harvey P. Dale, Jul 03 2020 *)

Extensions

More terms from Robert G. Wilson v, Jul 12 2010