21391669 has 8 divisors (see below), whose sum is σ = 23073120. Its totient is φ = 19715376.

The previous prime is 21391651. The next prime is 21391703. The reversal of 21391669 is 96619312.

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 21391669 - 2¹⁵ = 21358901 is a prime.

It is a super-2 number, since 2×21391669² = 915207005211122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391619) 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, 15714 + ... + 17020.

It is an arithmetic number, because the mean of its divisors is an integer number (2884140).

Almost surely, 2^21391669 is an apocalyptic number.

It is an amenable number.

21391669 is a deficient number, since it is larger than the sum of its proper divisors (1681451).

21391669 is a wasteful number, since it uses less digits than its factorization.

21391669 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2579.

The product of its digits is 17496, while the sum is 37.

The square root of 21391669 is about 4625.1128634878. The cubic root of 21391669 is about 277.5970777417.

The spelling of 21391669 in words is "twenty-one million, three hundred ninety-one thousand, six hundred sixty-nine".