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 A055257 #14 Apr 08 2025 12:40:40
%S A055257 2,7,12,37,42,72,217,222,252,432,1297,1302,1332,1512,2592,7777,7782,
%T A055257 7812,7992,9072,15552,46657,46662,46692,46872,47952,54432,93312,
%U A055257 279937,279942,279972,280152,281232,287712,326592,559872,1679617,1679622,1679652,1679832
%N A055257 Sums of two powers of 6.
%H A055257 T. D. Noe, <a href="/A055257/b055257.txt">Rows n = 0..100 of triangle, flattened</a>
%F A055257 a(n) = 6^(n-trinv(n))+6^trinv(n), where trinv(n) = floor((1+sqrt(1+8*n))/2) = A002262(n) and n-trinv(n) = A003056(n)
%F A055257 Regarded as a triangle T(n, k) = 6^n + 6^k, so as a sequence a(n) = 6^A002262(n) + 6^A003056(n).
%t A055257 t = 6^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* _T. D. Noe_, Oct 09 2011 *)
%o A055257 (Python)
%o A055257 from math import isqrt
%o A055257 def A055257(n): return 6**(a:=(k:=isqrt(m:=n<<1))+(m>k*(k+1))-1)+6**(n-1-(a*(a+1)>>1)) # _Chai Wah Wu_, Apr 08 2025
%Y A055257 Cf. A052216.
%K A055257 easy,nonn,tabl
%O A055257 0,1
%A A055257 _Henry Bottomley_, Jun 22 2000