21991401 has 12 divisors (see below), whose sum is σ = 31807620. Its totient is φ = 14641440.

The previous prime is 21991397. The next prime is 21991433. The reversal of 21991401 is 10419912.

It can be written as a sum of positive squares in 2 ways, for example, as 12257001 + 9734400 = 3501^2 + 3120^2 .

It is not a de Polignac number, because 21991401 - 2² = 21991397 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21991451) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9595 + ... + 11663.

It is an arithmetic number, because the mean of its divisors is an integer number (2650635).

Almost surely, 2^21991401 is an apocalyptic number.

It is an amenable number.

21991401 is a deficient number, since it is larger than the sum of its proper divisors (9816219).

21991401 is a wasteful number, since it uses less digits than its factorization.

21991401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3256 (or 3253 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 27.

The square root of 21991401 is about 4689.4990137540. The cubic root of 21991401 is about 280.1674211320.

It can be divided in two parts, 2199 and 1401, that added together give a square (3600 = 60²).

The spelling of 21991401 in words is "twenty-one million, nine hundred ninety-one thousand, four hundred one".