21851649 has 6 divisors (see below), whose sum is σ = 31563506. Its totient is φ = 14567760.

The previous prime is 21851629. The next prime is 21851657. The reversal of 21851649 is 94615812.

21851649 is a `hidden beast` number, since 2 + 1 + 8 + 5 + 1 + 649 = 666.

It can be written as a sum of positive squares in only one way, i.e., 19079424 + 2772225 = 4368^2 + 1665^2 .

It is not a de Polignac number, because 21851649 - 2⁷ = 21851521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21851629) by changing a digit.

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 5 ways as a sum of consecutive naturals, for example, 1213972 + ... + 1213989.

Almost surely, 2^21851649 is an apocalyptic number.

It is an amenable number.

21851649 is a deficient number, since it is larger than the sum of its proper divisors (9711857).

21851649 is a wasteful number, since it uses less digits than its factorization.

21851649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2427967 (or 2427964 counting only the distinct ones).

The product of its digits is 17280, while the sum is 36.

The square root of 21851649 is about 4674.5747400165. The cubic root of 21851649 is about 279.5726857831.

It can be divided in two parts, 21851 and 649, that added together give a square (22500 = 150²).

The spelling of 21851649 in words is "twenty-one million, eight hundred fifty-one thousand, six hundred forty-nine".