

A000864


Deceptive nonprimes: composite numbers n such that n divides the repunit R_{n1}.


3



91, 259, 451, 481, 703, 1729, 2821, 2981, 3367, 4141, 4187, 5461, 6533, 6541, 6601, 7471, 7777, 8149, 8401, 8911, 10001, 11111, 12403, 13981, 14701, 14911, 15211, 15841, 19201, 21931, 22321, 24013, 24661, 27613, 29341, 34133
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OFFSET

1,1


COMMENTS

Francis and Ray call these numbers "deceptive primes".
Pseudoprimes to base 10, A005939, indivisible by 3. If n is in the sequence, then (10^n1)/9 is in the sequence; by Steuerwald's theorem, see A005935.  Thomas Ordowski, Apr 10 2016
41041 is the first term that has four prime divisors.  Altug Alkan, Apr 10 2016


LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
R. Francis and T. Ray, The deceptive primes to 2.10^7, Missouri J. Math. Sci. 12 (2000), no. 3, 145158.


MAPLE

select(t > not isprime(t) and (10&^(t1)  1) mod (9*t) = 0, [seq(t, t=3..10^5, 2)]); # Robert Israel, Apr 10 2016


PROG

(PARI) p=5; forprime(q=7, 1e5, forstep(n=p+2, q2, 2, if(n%5 && Mod(10, 9*n)^(n1)==1, print1(n", "))); p=q) \\ Charles R Greathouse IV, Jul 31 2011


CROSSREFS

Cf. A002275, A005939.
Sequence in context: A225909 A051973 A290812 * A224460 A020441 A209255
Adjacent sequences: A000861 A000862 A000863 * A000865 A000866 A000867


KEYWORD

nonn


AUTHOR

Tim Ray (C268SCM(AT)SEMOVM.SEMO.EDU)


STATUS

approved



