A273892 Numbers starting with an even (decimal) digit.

0, 2, 4, 6, 8, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219

Offset: 1

Author

Giovanni Teofilatto, Jun 02 2016

Keywords

• nonn
• easy
• base

Comments

For positive terms, a number is a term iff the first digit is even. Therefore, for k > 0, there are 4 * 10^(k - 1) terms having precisely k digits. - David A. Corneth, Jun 02 2016

Also numbers such that when the leftmost digit is moved to the unit's place the result is divisible by 2. - Stefano Spezia, Jul 08 2025

Examples

			21 is a term because 2 is an even number. - _Altug Alkan_, Jun 02 2016
		

Links

• Bruno Berselli, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A004086, A005843.

Programs

Magma

[0] cat [n: n in [1..220] | IsEven(Intseq(n)[#Intseq(n)])]; // Bruno Berselli, Jun 15 2016

Mathematica

Select[Range[0, 219], EvenQ@ FromDigits@ Reverse@ IntegerDigits@ # &] (* or *) {0} ~ Join ~ Select[Range@ 219, EvenQ@ Floor[#/10^Floor@ Log10@ #] &] (* Michael De Vlieger, Jun 03 2016 *)

PARI

A004086(n) = eval(concat(Vecrev(Str(n)))); lista(nn) = for(n=0, nn, if(A004086(n) % 2 == 0, print1(n, ", "))); \\ Altug Alkan, Jun 02 2016

PARI

a(n)=if(n==1, return(0), n--; k = logint(9*n\4, 10)); n -= 4 * ((10^k - 1) / 9); n--; 2 * (n \ 10^k + 1)*10^k+n%10^k
is(n) = n==0||digits(n)[1]%2==0 \\ David A. Corneth, Jun 02 2016