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 A004667 #15 Jun 23 2018 07:25:37 %S A004667 1,3,9,21,63,159,441 %N A004667 Powers of 3 written in base 13. (Next term contains a non-decimal digit.) %t A004667 FromDigits[IntegerDigits[#,13]]&/@(3^Range[0,6]) (* _Harvey P. Dale_, Mar 05 2018 *) %o A004667 (PARI) apply( a(n, b=13, m=3)=fromdigits(digits(m^n, b)), [0..6]) \\ This implements one possible continuation of the sequence beyond n = 6: write digits in decimal and carry over (so CC4 -> 12*100 + 12*10 + 4 = 1324). - _M. F. Hasler_, Jun 22 2018 %Y A004667 Cf. A000079, A004643, ..., A004655: powers of 2 written in base 10, 4, 5, ..., 16. %Y A004667 Cf. A000244, A004656, A004658, A004659, ..., A004668: powers of 3 in base 10, 2, 4, 5, ..., 26. %K A004667 nonn,base %O A004667 0,2 %A A004667 _N. J. A. Sloane_