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%I #32 Sep 08 2022 08:46:17
%S 0,2,4,6,8,20,21,22,23,24,25,26,27,28,29,40,41,42,43,44,45,46,47,48,
%T 49,60,61,62,63,64,65,66,67,68,69,80,81,82,83,84,85,86,87,88,89,200,
%U 201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219
%N Numbers starting with an even (decimal) digit.
%C 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
%H Bruno Berselli, <a href="/A273892/b273892.txt">Table of n, a(n) for n = 1..1000</a>
%e 21 is a term because 2 is an even number. - _Altug Alkan_, Jun 02 2016
%t 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 *)
%o (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
%o (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
%o is(n) = n==0||digits(n)[1]%2==0 \\ _David A. Corneth_, Jun 02 2016
%o (Magma) [0] cat [n: n in [1..220] | IsEven(Intseq(n)[#Intseq(n)])]; // _Bruno Berselli_, Jun 15 2016
%Y Cf. A004086, A005843.
%K nonn,easy,base
%O 1,2
%A _Giovanni Teofilatto_, Jun 02 2016
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