721801

Appears in sequences

• Pseudoprimes to bases 2,5 and 7.at n=20A083736
• Pseudoprimes to bases 2, 3 and 5.at n=30A083737
• Pseudoprimes to bases 2,3 and 7.at n=27A083738
• Pseudoprimes to bases 2, 3, 5 and 7.at n=17A083739
• Pseudoprimes to bases 3,5 and 7.at n=19A083740
• Records in A111273.at n=27A113732
• Numbers of the form p*q, p and q prime with q=2*p-1.at n=23A129521
• Terms of A083737 which are not Carmichael numbers (A002997).at n=0A153580
• Pseudoprimes to bases 2,3,5 and 7 which are not Carmichael numbers (A002997).at n=0A153581
• Intersection of A001567 and A212502.at n=22A212601
• Composite numbers k such that k divides Fibonacci(k+1) or Fibonacci(k-1) and 2^(k-1) == 1 (mod k).at n=10A214434
• Fermat pseudoprimes n to base 3 for which sqrt(8*n + 1) is an integer.at n=33A217841
• Squarefree numbers (from A005117) with prime divisors in a 2p-1 progression.at n=25A231814
• Sequence of distinct least positive triangular numbers such that the arithmetic mean of the first n terms is also a triangular number. Initial term is 1.at n=27A236416
• Pyramidal centered square numbers.at n=24A237516
• Record values in A265388.at n=26A265395
• Smallest weak pseudoprime to all natural bases up to prime(n) that is not a Carmichael number.at n=2A285549
• Smallest weak pseudoprime to all natural bases up to prime(n) that is not a Carmichael number.at n=3A285549
• Fermat pseudoprimes to base 2 that are triangular.at n=19A293622
• The "non-residue" pseudoprimes: odd composite numbers n such that b(n)^((n-1)/2) == -1 (mod n), where base b(n) = A020649(n).at n=15A307767