21605947 has 24 divisors (see below), whose sum is σ = 25482240. Its totient is φ = 18155280.

The previous prime is 21605933. The next prime is 21605951. The reversal of 21605947 is 74950612.

It is not a de Polignac number, because 21605947 - 2¹¹ = 21603899 is a prime.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21605747) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 273454 + ... + 273532.

It is an arithmetic number, because the mean of its divisors is an integer number (1061760).

Almost surely, 2^21605947 is an apocalyptic number.

21605947 is a deficient number, since it is larger than the sum of its proper divisors (3876293).

21605947 is a wasteful number, since it uses less digits than its factorization.

21605947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 183 (or 160 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 21605947 is about 4648.2197667494. The cubic root of 21605947 is about 278.5208864944.

The spelling of 21605947 in words is "twenty-one million, six hundred five thousand, nine hundred forty-seven".