21665739 has 8 divisors (see below), whose sum is σ = 29236032. Its totient is φ = 14269640.

The previous prime is 21665737. The next prime is 21665767. The reversal of 21665739 is 93756612.

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

It is a cyclic number.

It is not a de Polignac number, because 21665739 - 2¹ = 21665737 is a prime.

It is a super-2 number, since 2×21665739² = 938808492832242, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21665697 and 21665706.

It is not an unprimeable number, because it can be changed into a prime (21665737) 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, 43257 + ... + 43754.

It is an arithmetic number, because the mean of its divisors is an integer number (3654504).

Almost surely, 2^21665739 is an apocalyptic number.

21665739 is a deficient number, since it is larger than the sum of its proper divisors (7570293).

21665739 is an equidigital number, since it uses as much as digits as its factorization.

21665739 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87097.

The product of its digits is 68040, while the sum is 39.

The square root of 21665739 is about 4654.6470328050. The cubic root of 21665739 is about 278.7775748090. Note that the first 3 decimals are identical.

The spelling of 21665739 in words is "twenty-one million, six hundred sixty-five thousand, seven hundred thirty-nine".