21550661 has 4 divisors (see below), whose sum is σ = 23509824. Its totient is φ = 19591500.

The previous prime is 21550657. The next prime is 21550667. The reversal of 21550661 is 16605512.

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 21550661 - 2² = 21550657 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21550661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21550667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 979565 + ... + 979586.

It is an arithmetic number, because the mean of its divisors is an integer number (5877456).

Almost surely, 2^21550661 is an apocalyptic number.

It is an amenable number.

21550661 is a deficient number, since it is larger than the sum of its proper divisors (1959163).

21550661 is a wasteful number, since it uses less digits than its factorization.

21550661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1959162.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21550661 is about 4642.2689495547. The cubic root of 21550661 is about 278.2831208100.

The spelling of 21550661 in words is "twenty-one million, five hundred fifty thousand, six hundred sixty-one".