621561 has 4 divisors (see below), whose sum is σ = 828752. Its totient is φ = 414372.

The previous prime is 621541. The next prime is 621583. The reversal of 621561 is 165126.

It is a happy number.

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 not a de Polignac number, because 621561 - 2¹⁴ = 605177 is a prime.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (621521) 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, 103591 + ... + 103596.

It is an arithmetic number, because the mean of its divisors is an integer number (207188).

2⁶²¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

621561 is a deficient number, since it is larger than the sum of its proper divisors (207191).

621561 is a wasteful number, since it uses less digits than its factorization.

621561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 207190.

The product of its digits is 360, while the sum is 21.

The square root of 621561 is about 788.3914002575. The cubic root of 621561 is about 85.3416926354.

Adding to 621561 its reverse (165126), we get a palindrome (786687).

The spelling of 621561 in words is "six hundred twenty-one thousand, five hundred sixty-one".