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A077571
Squarefree numbers obtained by repeating a single digit.
2
1, 2, 3, 5, 6, 7, 11, 22, 33, 55, 66, 77, 111, 222, 555, 777, 1111, 2222, 3333, 5555, 6666, 7777, 11111, 22222, 33333, 55555, 66666, 77777, 111111, 222222, 555555, 1111111, 2222222, 3333333, 5555555, 6666666, 7777777, 11111111, 22222222, 33333333
OFFSET
1,2
COMMENTS
From Robert Israel, Feb 26 2019: (Start)
If A002275(n) is not in the sequence, then there are no terms of length n.
2*A002275(n) and 5*A002275(n) are in the sequence if and only if A002275(n) is in the sequence.
3*A002275(n) and 6*A002275(n) are in the sequence if and only if A002275(n) is in the sequence and n is not divisible by 3.
7*A002275(n) is in the sequence if and only if A002275(n) is in the sequence and n is not divisible by 6. (End)
Intersection of A005117 and A010785. - Felix Fröhlich, Feb 26 2019
LINKS
EXAMPLE
66 and 6666 are members but 666 is not.
MAPLE
g:= proc(n) local r;
r:= (10^n-1)/9;
if not numtheory:-issqrfree(r) then NULL
elif n mod 6 = 0 then r, 2*r, 5*r
elif n mod 3 = 0 then r, 2*r, 5*r, 7*r
else r, 2*r, 3*r, 5*r, 6*r, 7*r
fi
end proc:
seq(g(n), n=1..10); # Robert Israel, Feb 26 2019
PROG
(PARI) is(n) = n>0 && vecmin(digits(n))==vecmax(digits(n)) && issquarefree(n) \\ Felix Fröhlich, Feb 26 2019
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Nov 11 2002
EXTENSIONS
Corrected and extended by Ray Chandler, Aug 12 2003
Offset changed by Robert Israel, Feb 26 2019
STATUS
approved