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 A226221 Numbers n such that 2^n mod n is not a power of 2. 2
 1, 2, 4, 8, 16, 18, 25, 27, 32, 35, 36, 42, 45, 49, 50, 54, 55, 64, 70, 75, 77, 81, 88, 91, 95, 98, 99, 100, 104, 105, 108, 110, 115, 117, 119, 121, 125, 128, 130, 135, 136, 140, 143, 147, 150, 152, 153, 155, 156, 160, 161, 162, 169, 171, 175, 180, 184, 187, 189, 190, 198, 200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS All terms beyond the first two are composite: this is a subsequence of A065090. LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 EXAMPLE 2^18 = 262144 = 10 mod 18 and 10 is not a power of 2, so 18 is in the sequence. MAPLE isA226221 := proc(n)     local m ;     if n <= 2 then         return true;     end if;     m := A015910(n) ;     if type(m, 'odd') or m = 0 then         true;     elif nops(numtheory[factorset](m))  >1 then         true;     else         false;     end if; end proc: A226221 := proc(n)     local a;     if n <= 2 then         n;     else         for a from procname(n-1)+1 do             if isA226221(a) then                 return a;             end if;         end do:     end if; end proc: seq(A226221(n), n=1..30) ; # R. J. Mathar, Jun 06 2013 PROG (PARI) ispow2(n)=n>0 && n==1<

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Last modified April 10 16:16 EDT 2021. Contains 342845 sequences. (Running on oeis4.)