21447945 has 24 divisors (see below), whose sum is σ = 37287432. Its totient is φ = 11404800.

The previous prime is 21447929. The next prime is 21447953. The reversal of 21447945 is 54974412.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 186624 + 21261321 = 432^2 + 4611^2 .

It is not a de Polignac number, because 21447945 - 2⁴ = 21447929 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 23905 + ... + 24785.

It is an arithmetic number, because the mean of its divisors is an integer number (1553643).

Almost surely, 2^21447945 is an apocalyptic number.

It is an amenable number.

21447945 is a deficient number, since it is larger than the sum of its proper divisors (15839487).

21447945 is a wasteful number, since it uses less digits than its factorization.

21447945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1433 (or 1430 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21447945 is about 4631.1926109805. The cubic root of 21447945 is about 277.8402935145.

The spelling of 21447945 in words is "twenty-one million, four hundred forty-seven thousand, nine hundred forty-five".