A070799 - OEIS

%I #6 Jun 24 2014 01:08:24

%S 4,9,14,19,20,24,29,31,34,39,42,44,48,49,53,54,59,64,65,69,74,75,79,

%T 82,84,86,88,89,94,97,99,104,108,109,111,114,116,119,124,129,130,133,

%U 134,139,140,141,144,149,150,152,154,157,159,163,164,167,169,174,179,180

%N Numbers of the form 6jk-j-k.

%C Equivalently, numbers n such that 6n+1 has a factor == 5 (mod 6).

%C These numbers, together with numbers of the form 6jk+j+k (A070043) are the numbers n for which 6n+1 is composite (A046954). If we also add in the numbers of the form 6jk+j-k (A046953), we get the numbers n such that 6n-1 and 6n+1 do not form a pair of twin primes (A067611).

%e 31 = 6*2*3 - 2 - 3. Equivalently, 6*31+1 = (6*2-1)*(6*3-1).

%t Select[Range[250], MemberQ[Mod[Take[Divisors[6#+1], {2, -2}], 6], 5]&]

%Y Cf. A070043, A046953, A046954, A067611.

%K nonn

%O 1,1

%A _Jon Perry_, May 05 2002

%E Edited by _Dean Hickerson_, May 07 2002