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A201015
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Composite numbers whose product of digits is 2.
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1
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12, 21, 112, 121, 1112, 1121, 1211, 11112, 11121, 11211, 12111, 21111, 111112, 121111, 211111, 1111112, 1111121, 1112111, 1121111, 1211111, 2111111, 11111112, 11111121, 11111211, 11112111, 11121111, 11211111, 12111111, 21111111, 111111112, 111111121, 111111211
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OFFSET
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1,1
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COMMENTS
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Complement of A107612 with respect to A199986. Subsequence of A199981 (composite numbers whose multiplicative digital root is 2).
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LINKS
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EXAMPLE
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Number 121 is in sequence because 1*2*1 = 2, and 121 = 11*11 is composite.
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MATHEMATICA
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Sort[Select[FromDigits/@Flatten[Table[Permutations[Join[{2}, PadRight[ {}, n, 1]]], {n, 10}], 1], CompositeQ]] (* Harvey P. Dale, Oct 23 2015 *)
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PROG
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(Python)
from sympy import isprime
def agen(maxdigits):
for digs in range(1, maxdigits+1):
for i in range(digs):
t = int("1"*(digs-1-i) + "2" + "1"*i)
if not isprime(t): yield t
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CROSSREFS
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Cf. A107612 (primes whose product of digits is 2), A199986 (numbers whose product of digits is 2).
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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