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A215477
Semiprimes with consecutive (ascending) digits.
2
4, 6, 9, 34, 123, 789, 901, 1234, 34567, 56789, 901234, 1234567, 7890123, 567890123, 12345678901, 345678901234567, 4567890123456789, 12345678901234567, 890123456789012345, 3456789012345678901, 456789012345678901234, 123456789012345678901234567, 1234567890123456789012345678901, 23456789012345678901234567890123
OFFSET
1,1
COMMENTS
This is to semiprimes A001358 as A006055 is to primes.
EXAMPLE
a(9) = 34567 because it is semiprime 13 * 2659, and (3,4,5,6,7) are consecutive ascending digits.
MAPLE
R:= 4, 6, 9: V:= [$1..9]:
for d from 2 to 50 do
V:= map(n -> 10*n + ((n+1) mod 10), V);
W:= select(t -> numtheory:-bigomega(t)=2, V);
R:= R, op(W);
od:
R; # Robert Israel, Nov 15 2023
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jonathan Vos Post, Aug 12 2012
EXTENSIONS
Corrected and extended by R. J. Mathar, Aug 13 2012
STATUS
approved