login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
All terms except 1 are even. - Robert Israel, Apr 07 2019
LINKS
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
end proc:
select(filter, [$1..1000]); # Robert Israel, Apr 07 2019
MATHEMATICA
filterQ[n_] := Length[Select[Divisors[5 n + 1], Mod[#, 5] == 1 || Mod[#, 5] == 4&]] == 2 && Length[Select[Divisors[5 n - 1], Mod[#, 5] == 4&]] == 1;
Select[Range[1000], filterQ] (* Jean-François Alcover, Aug 16 2020, after Robert Israel *)
CROSSREFS
A002822 results if the coefficient 5 in the definition above is replaced by 6.
Includes 2*A124518.
Sequence in context: A098807 A189562 A194372 * A264986 A140955 A111905
KEYWORD
nonn
AUTHOR
John W. Layman, Nov 30 2000
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 21 19:43 EDT 2024. Contains 373558 sequences. (Running on oeis4.)