21521457 has 40 divisors (see below), whose sum is σ = 33988416. Its totient is φ = 13553568.

The previous prime is 21521453. The next prime is 21521459. The reversal of 21521457 is 75412512.

It is not a de Polignac number, because 21521457 - 2² = 21521453 is a prime.

It is a super-2 number, since 2×21521457² = 926346222805698, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21521457.

It is not an unprimeable number, because it can be changed into a prime (21521453) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 128788 + ... + 128954.

Almost surely, 2^21521457 is an apocalyptic number.

21521457 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21521457 is a deficient number, since it is larger than the sum of its proper divisors (12466959).

21521457 is a wasteful number, since it uses less digits than its factorization.

21521457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 259 (or 250 counting only the distinct ones).

The product of its digits is 2800, while the sum is 27.

The square root of 21521457 is about 4639.1224385653. The cubic root of 21521457 is about 278.1573604900.

Adding to 21521457 its reverse (75412512), we get a palindrome (96933969).

The spelling of 21521457 in words is "twenty-one million, five hundred twenty-one thousand, four hundred fifty-seven".