A365429 - OEIS

%I #9 Oct 22 2023 16:44:05

%S 1,1,0,1,0,1,0,1,0,0,0,1,0,0,0,1,0,1,0,1,0,0,0,1,0,0,0,1,0,1,0,1,0,0,

%T 0,1,0,0,0,1,0,1,0,0,0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,1,0,0,0,1,0,1,0,0,

%U 0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,1,0,1,0,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1

%N a(n) = 1 if the divisors of n increase by a factor of at most 2, otherwise 0.

%H Antti Karttunen, <a href="/A365429/b365429.txt">Table of n, a(n) for n = 1..100000</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%F a(n) <= A322860(n). [Conjectured, see comment in A174973]

%o (PARI) A365429(n) = { my(d=divisors(n)); for(i=2, #d, if(d[i]>2*d[i-1], return(0))); (1); }; \\ From "is" function given in A174973

%Y Characteristic function of A174973.

%Y Cf. A322860.

%K nonn

%O 1

%A _Antti Karttunen_, Oct 22 2023