21657970 has 16 divisors (see below), whose sum is σ = 39068568. Its totient is φ = 8644480.

The previous prime is 21657959. The next prime is 21657971. The reversal of 21657970 is 7975612.

It can be written as a sum of positive squares in 4 ways, for example, as 14830201 + 6827769 = 3851^2 + 2613^2 .

It is not an unprimeable number, because it can be changed into a prime (21657971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3132 + ... + 7288.

Almost surely, 2^21657970 is an apocalyptic number.

21657970 is a deficient number, since it is larger than the sum of its proper divisors (17410598).

21657970 is a wasteful number, since it uses less digits than its factorization.

21657970 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4685.

The product of its (nonzero) digits is 26460, while the sum is 37.

The square root of 21657970 is about 4653.8124156438. The cubic root of 21657970 is about 278.7442490452.

The spelling of 21657970 in words is "twenty-one million, six hundred fifty-seven thousand, nine hundred seventy".