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A158725 Non-repdigit composite numbers not divisible by 2, 3, 5 or 11. 3
49, 91, 119, 133, 161, 169, 203, 217, 221, 247, 259, 287, 289, 299, 301, 323, 329, 343, 361, 371, 377, 391, 403, 413, 427, 437, 469, 481, 493, 497, 511, 527, 529, 533, 551, 553, 559, 581, 589, 611, 623, 629, 637, 667, 679, 689, 697, 703, 707, 713, 721, 731 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
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.
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.
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
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
FORMULA
a(n) ~ kn with k = 33/8. - Charles R Greathouse IV, Sep 08 2012
PROG
(PARI) is(n)=gcd(n, 330)==1&&!isprime(n)&&n%(10^#Str(n)\9) \\ Charles R Greathouse IV, Sep 08 2012
CROSSREFS
Sequence in context: A273937 A326257 A231275 * A090825 A350704 A157342
KEYWORD
nonn
AUTHOR
Lekraj Beedassy, Mar 24 2009
EXTENSIONS
Corrected and extended by Ray Chandler, Mar 27 2009
STATUS
approved

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Last modified July 13 23:31 EDT 2024. Contains 374290 sequences. (Running on oeis4.)