21157947 has 6 divisors (see below), whose sum is σ = 30561492. Its totient is φ = 14105292.

The previous prime is 21157933. The next prime is 21157957. The reversal of 21157947 is 74975112.

It is a happy number.

It is not a de Polignac number, because 21157947 - 2⁶ = 21157883 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21157957) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1175433 + ... + 1175450.

It is an arithmetic number, because the mean of its divisors is an integer number (5093582).

Almost surely, 2^21157947 is an apocalyptic number.

21157947 is a deficient number, since it is larger than the sum of its proper divisors (9403545).

21157947 is a wasteful number, since it uses less digits than its factorization.

21157947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2350889 (or 2350886 counting only the distinct ones).

The product of its digits is 17640, while the sum is 36.

The square root of 21157947 is about 4599.7768424131. The cubic root of 21157947 is about 276.5823792854.

The spelling of 21157947 in words is "twenty-one million, one hundred fifty-seven thousand, nine hundred forty-seven".