21871641 has 16 divisors (see below), whose sum is σ = 33488640. Its totient is φ = 12557520.

The previous prime is 21871631. The next prime is 21871667. The reversal of 21871641 is 14617812.

It is not a de Polignac number, because 21871641 - 2⁵ = 21871609 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21871599 and 21871608.

It is not an unprimeable number, because it can be changed into a prime (21871631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16815 + ... + 18068.

It is an arithmetic number, because the mean of its divisors is an integer number (2093040).

Almost surely, 2^21871641 is an apocalyptic number.

It is an amenable number.

21871641 is a deficient number, since it is larger than the sum of its proper divisors (11616999).

21871641 is a wasteful number, since it uses less digits than its factorization.

21871641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34916.

The product of its digits is 2688, while the sum is 30.

The square root of 21871641 is about 4676.7126274767. The cubic root of 21871641 is about 279.6579198308.

Adding to 21871641 its product of digits (2688), we get a square (21874329 = 4677²).

It can be divided in two parts, 2187 and 1641, that added together give a triangular number (3828 = T₈₇).

The spelling of 21871641 in words is "twenty-one million, eight hundred seventy-one thousand, six hundred forty-one".