A086982 Numbers n such that 10^n+1 is not squarefree.

11, 21, 33, 39, 55, 63, 77, 99, 105, 117, 121, 136, 143, 147, 165, 171, 187, 189, 195, 202, 209, 231, 243, 253, 273, 275, 292, 297, 315, 319, 341, 351, 357, 363, 385, 399, 406, 407, 408, 429, 441, 451, 473, 483, 495, 507, 513, 517, 525, 539, 548, 561, 567

Offset

1,1

Comments

This sequence is the union of the collection of sequences formed from the nonzero terms of A086981 * A005408, the odd numbers. First occurrence of consecutive integers in sequence is 406,407,408.

From Robert Israel, Feb 13 2017: (Start)

Numbers n such that gcd(n, 10^n + 1) > 1 or n = k m where k is odd and 2 m is the order of 2 modulo a member of A045616.

If n is in the sequence, then so is k*n for any odd k. (End)

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= n -> (n mod 243 = 0 and (n/243)::odd) or igcd(n, (10 &^n +1 mod n)) > 1: # Note that this works if n < 28299156
select(filter, [$1..1000]); # Robert Israel, Feb 13 2017

Crossrefs

Cf. A005408, A013929, A086981, A045616, A049096, A282344, A282345.

Sequence in context: A264646 A139113 A109335 * A145060 A146246 A215968

Adjacent sequences: A086979 A086980 A086981 * A086983 A086984 A086985

Keyword

nonn

Author

Ray Chandler, Jul 27 2003

Status

approved