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A063138 Composite numbers not divisible by 2, 3, 5 or 7 which in base 2 contain their largest proper factor as a substring. 2
407, 493, 893, 1189, 1343, 1403, 1643, 1681, 1961, 3151, 3223, 4063, 4579, 7087, 7597, 7979, 8791, 9167, 10579, 11227, 13303, 14219, 15487, 16147, 23479, 24341, 25751, 26101, 27571, 28757, 30461, 30607, 33431, 34093, 35417, 36349, 39917 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

EXAMPLE

407 is in the sequence because 407_d = 110010111_b and its largest proper divisor is 37_d = 100101_b is a substring. Also 407 is not prime nor congruent to 0 (modulo either 2, 3, 5 or 7).

MATHEMATICA

a = {}; Do[ If[ !PrimeQ[n] && Sort[Mod[n, {3, 5, 7}]][[1]] != 0 && StringPosition[ ToString[ FromDigits[ IntegerDigits[n, 2]]], ToString[ FromDigits[ IntegerDigits[ Divisors[n][[ -2]], 2]]]] != {}, a = Append[a, n]], {n, 3, 39960, 2}]; a

CROSSREFS

Cf. A002808, A062238.

Sequence in context: A203936 A172891 A172921 * A118327 A213606 A343157

Adjacent sequences:  A063135 A063136 A063137 * A063139 A063140 A063141

KEYWORD

base,nonn

AUTHOR

Robert G. Wilson v, Aug 08 2001; corrected Nov 13 2002

STATUS

approved

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Last modified October 27 02:00 EDT 2021. Contains 348270 sequences. (Running on oeis4.)