1621561 has 4 divisors (see below), whose sum is σ = 1630800. Its totient is φ = 1612324.

The previous prime is 1621559. The next prime is 1621583. The reversal of 1621561 is 1651261.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1621561 - 2¹ = 1621559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1621541) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4351 + ... + 4708.

It is an arithmetic number, because the mean of its divisors is an integer number (407700).

2^1621561 is an apocalyptic number.

It is an amenable number.

1621561 is a deficient number, since it is larger than the sum of its proper divisors (9239).

1621561 is an equidigital number, since it uses as much as digits as its factorization.

1621561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9238.

The product of its digits is 360, while the sum is 22.

The square root of 1621561 is about 1273.4052771997. The cubic root of 1621561 is about 117.4837400165.

The spelling of 1621561 in words is "one million, six hundred twenty-one thousand, five hundred sixty-one".