OFFSET
1,2
COMMENTS
All odd primes are in this sequence. This sequence contains almost all odd numbers.
Numbers k divisible by 2 but not by 4 are not members since U(k) is isomorphic to U(k/2) (i.e., 2, 6, 10, 14, ... are not terms).
Numbers k divisible by 4 but not by 3 or 8 are not members since U(k) is isomorphic to U(3/4*k) (i.e., 4, 20, 28, 44, ... are not terms).
Numbers k divisible by 12 but not by 24 or 36 are not members since U(k) is isomorphic to U(2/3*k) (i.e., 12, 60, 84, 132, ... are not terms).
Numbers k divisible by 9 but not by 7 or 27 are not members since U(k) is isomorphic to U(7/9*k) (i.e., 9, 18, 36, 45, 72, ... are not terms).
Numbers k divisible by 27 but not by 19 or 81 are not members since U(k) is isomorphic to U(19/27*k) (i.e., 27, 54, 108, 135, ... are not terms).
First term == 4 (mod 8) is 252.
LINKS
Jianing Song, Table of n, a(n) for n = 1..6527 (All terms <= 16384.)
Wikipedia, Multiplicative group of integers modulo n
FORMULA
a(n) = min{k : A289626(k) = n}. - Jianing Song, Jun 30 2018
EXAMPLE
75 is not a term because U(55) and U(75) are both isomorphic to C_2 x C_20.
93 is not a term because U(77) and U(93) are both isomorphic to C_2 x C_30.
96 is a term because U(96) is isomorphic to C_2 x C_2 x C_8 and U(k) is not isomorphic to C_2 x C_2 x C_8 for all k < 96.
PROG
(PARI) isA296233(n) = !(sum(i=1, n-1, znstar(i)[2]==znstar(n)[2])) \\ Jianing Song, Oct 04 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Jianing Song, Apr 29 2018
STATUS
approved