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A225508 -4-Knödel numbers. 9
4, 6, 8, 12, 14, 16, 20, 24, 40, 48, 56, 60, 66, 80, 104, 120, 140, 176, 204, 240, 260, 266, 476, 560, 696, 728, 920, 1020, 1040, 1292, 1508, 1634, 1736, 1820, 1976, 2320, 2544, 2660, 3416, 3440, 3848, 4136, 4686, 4756, 5180, 5456, 6188, 6608, 7280, 8004, 8816 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Extension of k-Knödel numbers to k negative, in this case equal to -4. Composite numbers n > 0 such that if 1 < a < n and gcd(n,a) = 1 then a^(n+4) = 1 mod n.

All terms are even numbers.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Knödel Numbers

MAPLE

with(numtheory); ListA225508:=proc(q, k) local a, n, ok;

for n from 2 to q do if not isprime(n) then ok:=1; for a from 1 to n do

if gcd(a, n)=1 then if (a^(n-k)-1) mod n<>0 then ok:=0; break; fi; fi;

od; if ok=1 then print(n); fi; fi; od; end: ListA225508(10^6, -4);

MATHEMATICA

Select[Range[10000], CompositeQ[#] && Divisible[# + 4, CarmichaelLambda[#]] &] (* Amiram Eldar, Mar 28 2019 *)

CROSSREFS

Cf. A208728.

Cf. A225506, A225507, A225509, A225510, A225511, A225512, A225513, A225514.

Sequence in context: A249722 A047407 A090697 * A235036 A107303 A028876

Adjacent sequences:  A225505 A225506 A225507 * A225509 A225510 A225511

KEYWORD

nonn

AUTHOR

Paolo P. Lava, May 09 2013

EXTENSIONS

More terms from Amiram Eldar, Mar 28 2019

STATUS

approved

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Last modified March 28 19:56 EDT 2020. Contains 333103 sequences. (Running on oeis4.)