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A201015
Composite numbers whose product of digits is 2.
1
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
OFFSET
1,1
COMMENTS
Complement of A107612 with respect to A199986. Subsequence of A199981 (composite numbers whose multiplicative digital root is 2).
LINKS
EXAMPLE
Number 121 is in sequence because 1*2*1 = 2, and 121 = 11*11 is composite.
MATHEMATICA
Select[Sort[Flatten[Table[FromDigits/@Permutations[PadRight[{2}, n, 1]], {n, 2, 9}]]], CompositeQ] (* Harvey P. Dale, Oct 06 2024 *)
PROG
(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
print(list(agen(9))) # Michael S. Branicky, Dec 21 2021
CROSSREFS
Cf. A107612 (primes whose product of digits is 2), A199986 (numbers whose product of digits is 2).
Sequence in context: A039402 A043225 A111066 * A044005 A321771 A225864
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 25 2011
STATUS
approved