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

1,2

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

Links

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

Example

21 is a term because 2 is an even number. - Altug Alkan, Jun 02 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 *)

Prog

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

Crossrefs

Cf. A004086, A005843.

Sequence in context: A076402 A053198 A249278 * A352546 A179082 A341869

Adjacent sequences: A273889 A273890 A273891 * A273893 A273894 A273895

Keyword

nonn,easy,base

Author

Giovanni Teofilatto, Jun 02 2016

Status

approved