21631421 has 16 divisors (see below), whose sum is σ = 25944576. Its totient is φ = 17646336.

The previous prime is 21631409. The next prime is 21631439. The reversal of 21631421 is 12413612.

It is a de Polignac number, because none of the positive numbers 2^k-21631421 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21631393 and 21631402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21631471) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11285 + ... + 13061.

It is an arithmetic number, because the mean of its divisors is an integer number (1621536).

Almost surely, 2^21631421 is an apocalyptic number.

It is an amenable number.

21631421 is a deficient number, since it is larger than the sum of its proper divisors (4313155).

21631421 is a wasteful number, since it uses less digits than its factorization.

21631421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1868.

The product of its digits is 288, while the sum is 20.

The square root of 21631421 is about 4650.9591483908. The cubic root of 21631421 is about 278.6303047404.

The spelling of 21631421 in words is "twenty-one million, six hundred thirty-one thousand, four hundred twenty-one".