cp's OEIS Frontend

A215138 Numbers n such that n > d(n)^2/2 where d = A000005.

%I A215138 #8 Jun 02 2025 08:06:28
%S A215138 1,3,5,7,9,10,11,13,14,15,16,17,19,20,21,22,23,25,26,27,28,29,31,32,
%T A215138 33,34,35,37,38,39,40,41,42,43,44,45,46,47,49,50,51,52,53,54,55,56,57,
%U A215138 58,59,61,62,63,64,65,66,67,68,69,70,71,73,74,75,76,77,78,79,80,81,82,83,84,85
%N A215138 Numbers n such that n > d(n)^2/2 where d = A000005.
%C A215138 n <= A000005(n)^2/2 begins: 2, 4, 6, 8, 12, 18, 24, 30, 36, 48, 60, 72, 120.
%e A215138 a(1)=1 because 1 > A000005(1)^2/2 = 1^2/2 = 1/2;
%e A215138 a(2)=3 because 3 > A000005(3)^2/2 = 2^2/2 = 2;
%e A215138 a(3)=5 because 5 > A000005(5)^2/2 = 2^2/2 = 2;
%e A215138 a(4)=7 because 7 > A000005(7)^2/2 = 2^2/2 = 2;
%e A215138 a(5)=9 because 9 > A000005(9)^2/2 = 3^2/2 = 9/2;
%e A215138 a(6)=10 because 10 > A000005(1)^2/2 = 4^2/2 =8.
%o A215138 (PARI) is(n)=numdiv(n)^2/2<n
%Y A215138 Cf. A035033, A035035.
%K A215138 nonn
%O A215138 1,2
%A A215138 _Gerasimov Sergey_, Aug 04 2012