OFFSET
1,1
COMMENTS
If k is in this sequence, then 2*k + 1 must be a square. So this sequence is a subsequence of A046092.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
3280 is a term because 3280 = 2^4 * 5 * 41 is divisible by d(3280) = 2^2 * 5 and 2 * 3280 + 1 = 3^8 is divisible by d(3^8) = 9.
MATHEMATICA
Select[Table[2 n (n + 1), {n, 10^4}], Times @@ Boole@ Thread[Divisible[#, DivisorSigma[0, #]] &@ {#, 2 # + 1}] > 0 &] (* Michael De Vlieger, Jan 19 2017 *)
PROG
(PARI) isA033950(n) = n % numdiv(n)== 0;
is(n) = isA033950(n) && isA033950(2*n+1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Jan 19 2017
STATUS
approved