21685953 has 4 divisors (see below), whose sum is σ = 28914608. Its totient is φ = 14457300.

The previous prime is 21685913. The next prime is 21685967. The reversal of 21685953 is 35958612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21685953 - 2¹⁷ = 21554881 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21685913) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3614323 + ... + 3614328.

It is an arithmetic number, because the mean of its divisors is an integer number (7228652).

Almost surely, 2^21685953 is an apocalyptic number.

It is an amenable number.

21685953 is a deficient number, since it is larger than the sum of its proper divisors (7228655).

21685953 is an equidigital number, since it uses as much as digits as its factorization.

21685953 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7228654.

The product of its digits is 64800, while the sum is 39.

The square root of 21685953 is about 4656.8179049647. The cubic root of 21685953 is about 278.8642471087.

The spelling of 21685953 in words is "twenty-one million, six hundred eighty-five thousand, nine hundred fifty-three".