A153519 Nonprime numbers k such that 10^k == 10 (mod k) and are not Carmichael numbers.

1, 6, 9, 10, 15, 18, 30, 33, 45, 55, 90, 91, 99, 165, 246, 259, 370, 385, 451, 481, 495, 505, 657, 703, 715, 909, 1035, 1045, 1233, 1626, 2035, 2409, 2981, 3333, 3367, 3585, 4005, 4141, 4187, 4521, 4545, 5005, 5461, 6533, 6541, 6565, 7107, 7471, 7777, 8149

Offset: 1

Author

Artur Jasinski, Dec 28 2008

Keywords

• nonn

Comments

Old name: Members of A121014 which are not Carmichael numbers A002997.

Links

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

Crossrefs

Cf. A002997, A122780, A153508, A153513, A153514, A153515.

Programs

Mathematica

Select[Range[8000], !PrimeQ[#] && PowerMod[10, #, #] == Mod[10, #] && !(# > 1 && Divisible[# - 1, CarmichaelLambda[#]]) &] (* Amiram Eldar, Mar 19 2020 *)

PARI

isok(n) = !isprime(n) && !is_A002997(n) && (Mod(10^n, n) == Mod(10, n)); \\ Michel Marcus, Nov 06 2013

Extensions

New name from Michel Marcus, Nov 06 2013