21649945 has 8 divisors (see below), whose sum is σ = 26167680. Its totient is φ = 17194800.

The previous prime is 21649931. The next prime is 21649961. The reversal of 21649945 is 54994612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21649945 - 2¹⁷ = 21518873 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21649898 and 21649907.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14881 + ... + 16270.

It is an arithmetic number, because the mean of its divisors is an integer number (3270960).

Almost surely, 2^21649945 is an apocalyptic number.

It is an amenable number.

21649945 is a deficient number, since it is larger than the sum of its proper divisors (4517735).

21649945 is a wasteful number, since it uses less digits than its factorization.

21649945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31295.

The product of its digits is 77760, while the sum is 40.

The square root of 21649945 is about 4652.9501394277. The cubic root of 21649945 is about 278.7098167793.

The spelling of 21649945 in words is "twenty-one million, six hundred forty-nine thousand, nine hundred forty-five".