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 A072390 #21 Apr 08 2025 13:58:43
%S A072390 2,14,26,170,182,338,2198,2210,2366,4394,28562,28574,28730,30758,
%T A072390 57122,371294,371306,371462,373490,399854,742586,4826810,4826822,
%U A072390 4826978,4829006,4855370,5198102,9653618,62748518,62748530,62748686,62750714,62777078,63119810,67575326,125497034
%N A072390 Sum of two powers of 13.
%H A072390 T. D. Noe, <a href="/A072390/b072390.txt">Rows n = 0..100 of triangle, flattened</a>
%F A072390 T(n,m) = 13^n + 13^m, n = 0, 1, 2, 3 ..., m = 0, 1, 2, 3, ... n.
%t A072390 Union[Total/@Tuples[13^Range[0,9], 2]] (* _Harvey P. Dale_, Sep 15 2011 *)
%t A072390 Flatten[Table[Table[13^n + 13^m, {m, 0, n}], {n, 0, 10}]] (* _T. D. Noe_, Jun 18 2013 *)
%o A072390 (Python)
%o A072390 def aupto(lim):
%o A072390 pows, p = [], 1
%o A072390 while p < lim: pows.append(p); p *= 13
%o A072390 return sorted([a+b for a in pows for b in pows if b >= a and a+b <= lim])
%o A072390 print(aupto(63119810)) # _Michael S. Branicky_, Feb 14 2021
%o A072390 (Python)
%o A072390 from math import isqrt
%o A072390 def A072390(n): return 13**(a:=(k:=isqrt(m:=n<<1))+(m>k*(k+1))-1)+13**(n-1-(a*(a+1)>>1)) # _Chai Wah Wu_, Apr 08 2025
%K A072390 easy,nonn,tabl
%O A072390 0,1
%A A072390 _Jeremy Gardiner_, Jul 20 2002