621661 has 4 divisors (see below), whose sum is σ = 654400. Its totient is φ = 588924.

The previous prime is 621641. The next prime is 621671. The reversal of 621661 is 166126.

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, and also an emirpimes, since its reverse is a distinct semiprime: 166126 = 2 ⋅83063.

It is not a de Polignac number, because 621661 - 2⁵ = 621629 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (621611) 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, 16341 + ... + 16378.

It is an arithmetic number, because the mean of its divisors is an integer number (163600).

2⁶²¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

621661 is a deficient number, since it is larger than the sum of its proper divisors (32739).

621661 is a wasteful number, since it uses less digits than its factorization.

621661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32738.

The product of its digits is 432, while the sum is 22.

The square root of 621661 is about 788.4548179826. The cubic root of 621661 is about 85.3462691300.

Adding to 621661 its reverse (166126), we get a palindrome (787787).

Subtracting from 621661 its reverse (166126), we obtain a triangular number (455535 = T₉₅₄).

The spelling of 621661 in words is "six hundred twenty-one thousand, six hundred sixty-one".