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 A286683 #32 Jun 25 2017 13:56:42 %S A286683 2,12,20,28,44,52,68,72,76,92,116,124,148,164,172,188,200,212,236,240, %T A286683 244,268,284,292,316,332,336,356,388,392,404,412,428,432,436,452,508, %U A286683 524,528,548,556,560,596,604,624,628,652,668,692,716,724,764,772,788,796,816 %N A286683 Even numbers k such that the number of odd divisors of k is equal to the 2-adic valuation of k. %C A286683 This sequence is infinite; 4 * p is in the sequence for odd prime p. - _David A. Corneth_, Jun 22 2017 %F A286683 a(n) = 2*A072978(n). %F A286683 A001227(a(n)) = A007814(a(n)). %e A286683 2 is in this sequence because A001227(2) = A007814(2) = 1. %e A286683 240 is in the sequence because 240 has 4 odd divisors; they are 1, 3, 5 and 15. Furthermore, 240 = 2^4 * 3 * 5. - _David A. Corneth_, Jun 22 2017 %t A286683 Select[Range@ 820, DivisorSum[#, 1 &, OddQ] == IntegerExponent[#, 2] &] (* _Michael De Vlieger_, Jun 22 2017 *) %o A286683 (PARI) is(n) = my(v); n%2==0 && v=valuation(n, 2); numdiv(n>>v)==v \\ _David A. Corneth_, Jun 22 2017 %Y A286683 Cf. A001227, A007814, A072978. %K A286683 nonn,easy %O A286683 1,1 %A A286683 _Juri-Stepan Gerasimov_, Jun 22 2017 %E A286683 More terms from _Michael De Vlieger_, Jun 22 2017 %E A286683 240 and 336 inserted by _David A. Corneth_, Jun 22 2017