21519657 has 12 divisors (see below), whose sum is σ = 31124340. Its totient is φ = 14327808.

The previous prime is 21519599. The next prime is 21519677. The reversal of 21519657 is 75691512.

It can be written as a sum of positive squares in 2 ways, for example, as 9884736 + 11634921 = 3144^2 + 3411^2 .

It is not a de Polignac number, because 21519657 - 2⁸ = 21519401 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21519677) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11833 + ... + 13529.

It is an arithmetic number, because the mean of its divisors is an integer number (2593695).

Almost surely, 2^21519657 is an apocalyptic number.

It is an amenable number.

21519657 is a deficient number, since it is larger than the sum of its proper divisors (9604683).

21519657 is a wasteful number, since it uses less digits than its factorization.

21519657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3112 (or 3109 counting only the distinct ones).

The product of its digits is 18900, while the sum is 36.

The square root of 21519657 is about 4638.9284322999. The cubic root of 21519657 is about 278.1496054821.

The spelling of 21519657 in words is "twenty-one million, five hundred nineteen thousand, six hundred fifty-seven".