cp's OEIS Frontend

A103154 Each letter appears an even number of times in the English names for 1 through n taken together (names without "and").

%I A103154 #9 Mar 17 2020 21:17:45
%S A103154 119,139,159,179,199,319,339,359,379,399,519,539,559,579,599,719,739,
%T A103154 759,779,799,919,939,959,979,999,1119,1139,1159,1179,1199,1319,1339,
%U A103154 1359,1379,1399,1519,1539,1559,1579,1599,1719,1739,1759,1779,1799,1919
%N A103154 Each letter appears an even number of times in the English names for 1 through n taken together (names without "and").
%H A103154 Robert Israel, <a href="/A103154/b103154.txt">Table of n, a(n) for n = 1..10000</a>
%F A103154 It appears that a(n+5)=a(n)+200. - _Robert Israel_, Mar 17 2020
%e A103154 Together the English words for 1 through 119 contain 40 d's, 218 e's, 56 f's, 22 g's, 64 h's, 100 i's, 4 l's, 144 n's, 62 o's, 64 r's, 44 s's, 150 t's, 32 u's, 36 v's, 22 w's, 22 x's and 80 y's. All counts are even so 119 is in the sequence.
%p A103154 letters:= [$"a".."z"]:
%p A103154 V:= Vector(26):
%p A103154 Res:= NULL: count:= 0:
%p A103154 for n from 1 while count < 100 do
%p A103154   S:= convert(n,english);
%p A103154   V:= V + <seq(StringTools:-CountCharacterOccurrences(S,letters[i]),i=1..26)>;
%p A103154   if andmap(type,V,even) then
%p A103154     count:= count+1; Res:= Res, n;
%p A103154   fi
%p A103154 od:
%p A103154 Res; # _Robert Israel_, Mar 17 2020
%K A103154 nonn,word
%O A103154 1,1
%A A103154 _David W. Wilson_, Jan 24 2005