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A158725 Non-repdigit composite numbers not divisible by 2, 3, 5 or 11. 3

%I

%S 49,91,119,133,161,169,203,217,221,247,259,287,289,299,301,323,329,

%T 343,361,371,377,391,403,413,427,437,469,481,493,497,511,527,529,533,

%U 551,553,559,581,589,611,623,629,637,667,679,689,697,703,707,713,721,731

%N Non-repdigit composite numbers not divisible by 2, 3, 5 or 11.

%C Non-repdigit composite numbers ending in 1, 3, 7 or 9, with digital root not a multiple of 3 and whose alternate digit sums do not differ by a multiple of 11.

%C The "compositeness" of larger entries of the sequence is not obvious right away or deducible by mere inspection, and hence these terms readily lend themselves to be (erroneously) suspected as primes to the casual glance.

%C This differs from the corresponding sequence without the repunit condition starting at a(1351) = 11123 rather than 11111. - _Charles R Greathouse IV_, Sep 08 2012

%H Charles R Greathouse IV, <a href="/A158725/b158725.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) ~ kn with k = 33/8. - _Charles R Greathouse IV_, Sep 08 2012

%o (PARI) is(n)=gcd(n,330)==1&&!isprime(n)&&n%(10^#Str(n)\9) \\ _Charles R Greathouse IV_, Sep 08 2012

%Y Cf. A007775, A053795, A008364.

%K nonn

%O 1,1

%A _Lekraj Beedassy_, Mar 24 2009

%E Corrected and extended by _Ray Chandler_, Mar 27 2009

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Last modified June 24 10:36 EDT 2021. Contains 345416 sequences. (Running on oeis4.)