21552661 has 4 divisors (see below), whose sum is σ = 23210572. Its totient is φ = 19894752.

The previous prime is 21552659. The next prime is 21552667. The reversal of 21552661 is 16625512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8520561 + 13032100 = 2919^2 + 3610^2 .

It is a cyclic number.

It is not a de Polignac number, because 21552661 - 2¹ = 21552659 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 (21552667) 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, 828936 + ... + 828961.

It is an arithmetic number, because the mean of its divisors is an integer number (5802643).

Almost surely, 2^21552661 is an apocalyptic number.

It is an amenable number.

21552661 is a deficient number, since it is larger than the sum of its proper divisors (1657911).

21552661 is a wasteful number, since it uses less digits than its factorization.

21552661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1657910.

The product of its digits is 3600, while the sum is 28.

The square root of 21552661 is about 4642.4843564626. The cubic root of 21552661 is about 278.2917291929.

The spelling of 21552661 in words is "twenty-one million, five hundred fifty-two thousand, six hundred sixty-one".