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 A212794 #16 Jul 29 2023 05:04:37 %S A212794 10,15,45,55,78,91,105,120,136,153,190,210,300,325,351,406,435,465, %T A212794 561,595,630,666,703,741,780,820,861,990,1035,1225,1275,1326,1378, %U A212794 1431,1485,1540,1653,1711,1770,1830,1891,2080,2145,2278,2346,2415,2485,2628 %N A212794 Triangular numbers (A000217) which are also hypotenuse numbers (A009003). %H A212794 Robert Israel, <a href="/A212794/b212794.txt">Table of n, a(n) for n = 1..10000</a> %p A212794 ishyp:= proc(n) ormap(t -> t mod 4 = 1, numtheory:-factorset(n)) end proc: %p A212794 select(ishyp, [seq(i*(i+1)/2, i=1..100)]); # _Robert Israel_, Jun 02 2023 %t A212794 A212794list[upto_]:=Select[PolygonalNumber[Range[4,upto]],AnyTrue[Map[Mod[First[#],4]==1&,FactorInteger[#]],TrueQ]&];A212794list[100] (* _Paolo Xausa_, Jul 28 2023 *) %o A212794 (PARI) for(n=1,99, is_A009003(A000217(n)) & print1(A000217(n)",")) %o A212794 (PARI) is_A212794(n) = is_A000217(n) & is_A009003(n) %Y A212794 Intersection of A000217 and A009003. %K A212794 nonn %O A212794 1,1 %A A212794 _M. F. Hasler_, May 27 2012