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 A004668 #22 Jun 22 2018 21:29:17 %S A004668 1,3,9,11,33,99,121,363 %N A004668 Powers of 3 written in base 26. (Next term contains a non-decimal digit.) %C A004668 Aliquot divisors of 1089. - _Omar E. Pol_, Jun 10 2014 %C A004668 The above comment refers to the first 8 terms only. The next term would contain a digit 18, commonly coded as I, if A, B, ... are used for digits > 9. But this does not mean that the sequence is finite. Many other encodings of digits > 9 are conceivable (e.g., using 000, 100, 110, ..., 250 for digits 0, 10, 11, ..., 25). - _M. F. Hasler_, Jun 22 2018 %t A004668 Select[Divisors[1089], # < 1089 &] (* _Wesley Ivan Hurt_, Jun 13 2014 *) %o A004668 (PARI) fordiv(1089, d, (d<1089) && print1(d, ", ")) \\ _Michel Marcus_, Jun 14 2014 %o A004668 (PARI) divisors(1089)[^-1] \\ _M. F. Hasler_, Jun 22 2018 %o A004668 (PARI) apply( A004668(n,b=26,m=3)=fromdigits(digits(m^n,b)), [0..8]) \\ This implements one possible continuation of the sequence beyond n = 7: write digits in decimal and carry over (so 363*3 = 9I9[26] -> 9*100 + 18*10 + 9 = 1089). - _M. F. Hasler_, Jun 22 2018 %Y A004668 Cf. A000244, A004656, A004658, A004659, ..., A004667: powers of 3 in base 10, 2, 4, 5, ..., 13. %Y A004668 Cf. A000079, A004643, ..., A004655: powers of 2 written in base 10, 4, 5, ..., 16. %K A004668 nonn,base %O A004668 0,2 %A A004668 _N. J. A. Sloane_, Dec 11 1996