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 A212315 #13 Mar 04 2023 19:29:00 %S A212315 0,1,3,7,15,31,39,45,63,78,79,91,93,127,139,143,158,159,175,182,187, %T A212315 189,222,255,286,287,318,319,351,367,375,379,381,407,446,487,511,535, %U A212315 543,572,574,575,607,627,638,639,703,724,727,731,747,750,759,763,765,799,823,830 %N A212315 Numbers m such that B(m) = B(triangular(m)), where B(m) is the binary weight of m (A000120). %H A212315 Dumitru Damian, <a href="/A212315/b212315.txt">Table of n, a(n) for n = 1..10000</a> %F A212315 A000120(a(n)) = A000120(a(n)*(a(n)+1)/2). %o A212315 (Python) %o A212315 def isa(n): return n.bit_count()==((n*(n+1))>>1).bit_count() %o A212315 print(list(n for n in range(10**3) if isa(n))) # _Dumitru Damian_, Mar 04 2023 %Y A212315 Cf. A000120, A077436, A083567, A118655, A212314. %K A212315 nonn,base,easy %O A212315 1,3 %A A212315 _Alex Ratushnyak_, Oct 24 2013