6421561 has 2 divisors, whose sum is σ = 6421562. Its totient is φ = 6421560.

The previous prime is 6421559. The next prime is 6421567. The reversal of 6421561 is 1651246.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6125625 + 295936 = 2475^2 + 544^2 .

It is a cyclic number.

It is not a de Polignac number, because 6421561 - 2¹ = 6421559 is a prime.

Together with 6421559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (6421567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3210780 + 3210781.

It is an arithmetic number, because the mean of its divisors is an integer number (3210781).

Almost surely, 2^6421561 is an apocalyptic number.

It is an amenable number.

6421561 is a deficient number, since it is larger than the sum of its proper divisors (1).

6421561 is an equidigital number, since it uses as much as digits as its factorization.

6421561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 25.

The square root of 6421561 is about 2534.0799119207. The cubic root of 6421561 is about 185.8718140175.

The spelling of 6421561 in words is "six million, four hundred twenty-one thousand, five hundred sixty-one".