This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A376856 #7 Oct 10 2024 20:46:33 %S A376856 1,2,3,5,11,22,33,44,121,222,101,202,454,1221,2222,1001,2002,4554, %T A376856 12221,22222,10001,20002,45554,122221,222222,100001,200002,455554, %U A376856 1222221,2222222,1000001,2000002,4555554,12222221,22222222,10000001,20000002,45555554,122222221,222222222,100000001,200000002,455555554,1222222221,2222222222,1000000001 %N A376856 a(1) = 1; for n > 1, a(n) is the smallest unused positive number such that a(n), |a(n) - a(n-1)| and a(1) + ... +a(n) are all palindromes. %C A376856 The sequence is infinite as from a(13) onward a repetitive pattern of five numbers appears, 45...54, 12...21, 22...22, 10...01, 20...02, all of which grow by one extra digit each iteration. %e A376856 a(9) = 121 as 121 is a palindrome, |121 - 44| = 77 is a palindrome, and 1 + 2 + 3 + 5 + 11 + 22 + 33 + 44 + 121 = 242 is a palindrome. %Y A376856 Cf. A073880, A073879, A002113, A369127, A361335, A347402. %K A376856 nonn,base %O A376856 1,2 %A A376856 _Scott R. Shannon_, Oct 06 2024