21896721 has 48 divisors (see below), whose sum is σ = 41533440. Its totient is φ = 10769760.

The previous prime is 21896717. The next prime is 21896767. The reversal of 21896721 is 12769812.

It is not a de Polignac number, because 21896721 - 2² = 21896717 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21895721) 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 47 ways as a sum of consecutive naturals, for example, 12336 + ... + 13998.

It is an arithmetic number, because the mean of its divisors is an integer number (865280).

Almost surely, 2^21896721 is an apocalyptic number.

21896721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21896721 is a deficient number, since it is larger than the sum of its proper divisors (19636719).

21896721 is a wasteful number, since it uses less digits than its factorization.

21896721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1706 (or 1703 counting only the distinct ones).

The product of its digits is 12096, while the sum is 36.

The square root of 21896721 is about 4679.3932298964. The cubic root of 21896721 is about 279.7647726795.

The spelling of 21896721 in words is "twenty-one million, eight hundred ninety-six thousand, seven hundred twenty-one".