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A105991 Semiprimes consisting of digits 0 and 1 only. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This includes repunit semiprimes also.

Intersection of A001358 (semiprimes) and A007088 (numbers written in base 2). - Michel Marcus, Jan 27 2015

LINKS

Zak Seidov, Table of n, a(n) for n = 1..531

EXAMPLE

a(3)=1011 is a term because 1011 is a semiprime and contain digits 0 and 1 only.

MAPLE

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

PROG

(PARI) isok(n) = (bigomega(n)==2) && (vecmax(digits(n)) <= 1); \\ Michel Marcus, Jan 27 2015

CROSSREFS

Cf. A001358, A007088.

Sequence in context: A257344 A244859 A159551 * A284352 A103581 A290232

Adjacent sequences:  A105988 A105989 A105990 * A105992 A105993 A105994

KEYWORD

base,nonn

AUTHOR

Shyam Sunder Gupta, Apr 29 2005

EXTENSIONS

Data corrected by Zak Seidov, Jan 27 2015

STATUS

approved

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Last modified August 25 16:31 EDT 2019. Contains 326324 sequences. (Running on oeis4.)