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Palindromes whose digit sum is 4.
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%I #8 Nov 27 2019 01:13:58

%S 4,22,121,202,1111,2002,10201,11011,20002,101101,110011,200002,

%T 1002001,1010101,1100011,2000002,10011001,10100101,11000011,20000002,

%U 100020001,100101001,101000101,110000011,200000002,1000110001,1001001001

%N Palindromes whose digit sum is 4.

%C There are ceiling(k/2) terms with k digits and so floor(n^2/4) terms with fewer than k digits. Writing the terms as a vertical column and then blanking zeros produces a narrow triangle with upward chevrons.

%Y Cf. A062397 and A066138 for digit sums of 2 and 3.

%K base,nonn

%O 1,1

%A _Henry Bottomley_, Dec 10 2001