A102884 a(n) * 6 does not appear in A102883.

5, 14, 18, 28, 44, 48, 52, 54, 55, 56, 68, 72, 76, 77, 85, 88, 91, 92, 95, 96, 104, 119, 125, 133, 145, 153, 154, 168, 171, 175, 182, 187, 190, 200, 203, 207, 209, 217, 222, 225, 230, 234, 238, 240, 245, 246, 248, 250, 253, 258, 261, 264, 266, 275, 279, 282, 287

Offset: 1

Author

Chuck Seggelin (seqfan(AT)plastereddragon.com), Jan 15 2005

Keywords

• nonn

Comments

Many of these are excluded because the sum of a(n)*6 and its divisors less than or equal to its square root is prime, but not always. a(3) = 18. 18*6 = 108. Adding the divisors less than or equal to the square root of 108 yields 133. 133 is not prime, but shares no common divisor with 108 greater than 1.

Examples

			a(2) = 14 because 14*6 is 84. The divisors of 84 which are less than or equal to its square root are 1, 2, 3, 4, 6 and 7. 84+1+2+3+4+6+7 = 107. GCD(84,107)=1, so 84 is excluded from A102883. Most multiples of 6 are included in A102883, 14*6 is the second multiple to be excluded.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A102883.

Programs

Mathematica

aQ[n_] := GCD[6n, DivisorSum[6n, # &, # < Sqrt[6n] &]] == 1; Select[Range[287], aQ] (* Amiram Eldar, Aug 28 2019 *)