21191257 has 8 divisors (see below), whose sum is σ = 22875840. Its totient is φ = 19570320.

The previous prime is 21191239. The next prime is 21191263. The reversal of 21191257 is 75219112.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21191257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21191557) 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, 15219 + ... + 16552.

It is an arithmetic number, because the mean of its divisors is an integer number (2859480).

Almost surely, 2^21191257 is an apocalyptic number.

It is an amenable number.

21191257 is a deficient number, since it is larger than the sum of its proper divisors (1684583).

21191257 is a wasteful number, since it uses less digits than its factorization.

21191257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31823.

The product of its digits is 1260, while the sum is 28.

The square root of 21191257 is about 4603.3962462512. The cubic root of 21191257 is about 276.7274489445.

The spelling of 21191257 in words is "twenty-one million, one hundred ninety-one thousand, two hundred fifty-seven".