21651621 has 8 divisors (see below), whose sum is σ = 30388320. Its totient is φ = 13674672.

The previous prime is 21651607. The next prime is 21651667. The reversal of 21651621 is 12615612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21651621 - 2⁵ = 21651589 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21651591 and 21651600.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651691) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 189870 + ... + 189983.

It is an arithmetic number, because the mean of its divisors is an integer number (3798540).

Almost surely, 2^21651621 is an apocalyptic number.

It is an amenable number.

21651621 is a deficient number, since it is larger than the sum of its proper divisors (8736699).

21651621 is a wasteful number, since it uses less digits than its factorization.

21651621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 379875.

The product of its digits is 720, while the sum is 24.

The square root of 21651621 is about 4653.1302367331. The cubic root of 21651621 is about 278.7170085697.

The spelling of 21651621 in words is "twenty-one million, six hundred fifty-one thousand, six hundred twenty-one".