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A105991
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Semiprimes consisting of digits 0 and 1 only.
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1
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10, 111, 1011, 1101, 1111, 10001, 11101, 11111, 100001, 101011, 110101, 110111, 111001, 111011, 111101, 1000001, 1000011, 1000101, 1000111, 1001001, 1001101, 1001111, 1010001, 1010111, 1100111, 1101011, 1110001, 1110011, 1110101, 1111001, 1111111, 10000001
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refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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This includes repunit semiprimes also.
Intersection of A001358 (semiprimes) and A007088 (numbers written in base 2). - Michel Marcus, Jan 27 2015
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LINKS
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Zak Seidov, Table of n, a(n) for n = 1..531
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EXAMPLE
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a(3)=1011 is a term because 1011 is a semiprime and contain digits 0 and 1 only.
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MAPLE
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N:= 12: # to get all terms with at most N digits
cands[1]:= {1}:
for d from 2 to N do
cands[d]:= map(t -> (10*t, 10*t+1), cands[d-1])
od:
select(numtheory:-bigomega = 2, `union`(seq(cands[d], d=1..N)));
# if using Maple 11 or lower, uncomment the next line
# sort(convert(%, list)); # Robert Israel, Jan 27 2015
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PROG
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(PARI) isok(n) = (bigomega(n)==2) && (vecmax(digits(n)) <= 1); \\ Michel Marcus, Jan 27 2015
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CROSSREFS
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Cf. A001358, A007088.
Sequence in context: A257344 A244859 A159551 * A284352 A103581 A290232
Adjacent sequences: A105988 A105989 A105990 * A105992 A105993 A105994
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KEYWORD
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base,nonn
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AUTHOR
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Shyam Sunder Gupta, Apr 29 2005
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EXTENSIONS
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Data corrected by Zak Seidov, Jan 27 2015
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STATUS
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approved
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