21026661 has 4 divisors (see below), whose sum is σ = 28035552. Its totient is φ = 14017772.

The previous prime is 21026657. The next prime is 21026689. The reversal of 21026661 is 16662012.

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 21026661 - 2² = 21026657 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21026641) 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, 3504441 + ... + 3504446.

It is an arithmetic number, because the mean of its divisors is an integer number (7008888).

Almost surely, 2^21026661 is an apocalyptic number.

It is an amenable number.

21026661 is a deficient number, since it is larger than the sum of its proper divisors (7008891).

21026661 is an equidigital number, since it uses as much as digits as its factorization.

21026661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7008890.

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21026661 is about 4585.4837258462. The cubic root of 21026661 is about 276.0091233069.

Adding to 21026661 its reverse (16662012), we get a palindrome (37688673).

The spelling of 21026661 in words is "twenty-one million, twenty-six thousand, six hundred sixty-one".