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 A086982 Numbers n such that 10^n+1 is not squarefree. 6
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified December 12 23:21 EST 2019. Contains 329963 sequences. (Running on oeis4.)