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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

Cf. A007775, A053795, A008364.

Sequence in context: A273937 A326257 A231275 * A090825 A157342 A230226

Adjacent sequences:  A158722 A158723 A158724 * A158726 A158727 A158728

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 May 8 09:16 EDT 2021. Contains 343666 sequences. (Running on oeis4.)