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

1,1

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.

Links

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

Example

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.

Mathematica

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

Crossrefs

Cf. A102883.

Sequence in context: A230091 A053782 A296692 * A356873 A071852 A275809

Adjacent sequences: A102881 A102882 A102883 * A102885 A102886 A102887

Keyword

nonn

Author

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

Status

approved