204001

Appears in sequences

• Composite numbers k such that 2^k-2 and 3^k-3 are both divisible by k and k is not a Carmichael number (A002997).at n=12A153513
• Numbers m such that exactly half of the a such that 0<a<m and (a,m)=1 satisfy a^(m-1) == 1 (mod m).at n=30A191311
• Numbers in A191311 but not in A129521.at n=15A191592
• Composite integers k such that 2^k == 2 (mod k*(k+1)).at n=27A217465
• a(n) = 2^n+(1+(n mod 2)/2)*C(n+1,floor((n+(n mod 2))/2))-1.at n=17A261682
• a(n) is the smallest n-gonal number that is a Fermat pseudoprime to base 2 (A001567), or -1 if no such number exists.at n=10A371759