21890961 has 12 divisors (see below), whose sum is σ = 32217588. Its totient is φ = 14318304.

The previous prime is 21890959. The next prime is 21890987. The reversal of 21890961 is 16909812.

It can be written as a sum of positive squares in 2 ways, for example, as 9884736 + 12006225 = 3144^2 + 3465^2 .

It is not a de Polignac number, because 21890961 - 2¹ = 21890959 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 (21890461) 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 11 ways as a sum of consecutive naturals, for example, 22470 + ... + 23423.

It is an arithmetic number, because the mean of its divisors is an integer number (2684799).

Almost surely, 2^21890961 is an apocalyptic number.

It is an amenable number.

21890961 is a deficient number, since it is larger than the sum of its proper divisors (10326627).

21890961 is a wasteful number, since it uses less digits than its factorization.

21890961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45952 (or 45949 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21890961 is about 4678.7777250047. Note that the first 4 decimals coincide. The cubic root of 21890961 is about 279.7402395328.

The spelling of 21890961 in words is "twenty-one million, eight hundred ninety thousand, nine hundred sixty-one".