A102883 -id:A102883 - cp's OEIS frontend

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

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

nonn

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.

			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.

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

Cf. A102883.

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

cp's OEIS Frontend

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

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