21253947 has 48 divisors (see below), whose sum is σ = 34714368. Its totient is φ = 11456640.

The previous prime is 21253943. The next prime is 21253957. The reversal of 21253947 is 74935212.

It is not a de Polignac number, because 21253947 - 2² = 21253943 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

Its product of digits (15120) is a multiple of the sum of its prime factors (180).

It is not an unprimeable number, because it can be changed into a prime (21253943) 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 47 ways as a sum of consecutive naturals, for example, 206298 + ... + 206400.

It is an arithmetic number, because the mean of its divisors is an integer number (723216).

Almost surely, 2^21253947 is an apocalyptic number.

21253947 is a deficient number, since it is larger than the sum of its proper divisors (13460421).

21253947 is a wasteful number, since it uses less digits than its factorization.

21253947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 180 (or 167 counting only the distinct ones).

The product of its digits is 15120, while the sum is 33.

The square root of 21253947 is about 4610.2003210273. The cubic root of 21253947 is about 277.0000608201. Note that the first 4 decimals are identical.

The spelling of 21253947 in words is "twenty-one million, two hundred fifty-three thousand, nine hundred forty-seven".