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A058218

Positive integers that cannot be represented in the form n=5|ab|+a+b for any choice of nonzero integers a and b (positive or negative).

1, 2, 4, 6, 8, 10, 12, 14, 18, 22, 26, 28, 30, 32, 36, 40, 44, 48, 50, 54, 58, 60, 62, 66, 76, 78, 82, 84, 94, 96, 98, 100, 102, 104, 114, 116, 120, 126, 132, 136, 138, 140, 144, 150, 154, 158, 162, 166, 170, 176, 184, 188, 190, 198, 202, 204, 208, 210, 212, 216, 220

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OFFSET

1,2

COMMENTS

All terms except 1 are even. - Robert Israel, Apr 07 2019

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Maria Suzuki, Related to Alternative Formulations of the Twin Prime Problem, American Math. Monthly, 107 (2000) pp. 55-56.

MAPLE

filter:= proc(n)

nops(select(t -> t mod 5 = 1 or t mod 5 = 4, numtheory:-divisors(5*n+1))) = 2

and nops(select(t -> t mod 5 = 4, numtheory:-divisors(5*n-1)))=1