A072864 - OEIS

%I #9 Nov 21 2013 10:44:00

%S 7,13,14,19,21,26,28,31,35,37,38,39,42,43,52,56,57,61,62,63,65,67,70,

%T 73,74,76,77,78,79,84,86,91,93,95,97,103,104,105,109,111,112,114,117,

%U 119,122,124,126,127,129,130,133,134,139,140,143,146,148,151,152,154

%N Numbers n such that the smallest k dividing sigma(k*n^2) is equal to 3.

%C Sequence contains primes of the form 6x+1 (A002476) and multiples of those primes, except (6x+1)^2. If x is not in the sequence, the smallest k dividing sigma(k*x^2) is equal to 6.

%o (PARI) isok(n) = A049605(n^2) != 6; \\ _Michel Marcus_, Nov 21 2013

%Y Cf. A049605.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Jul 27 2002