21720671 has 12 divisors (see below), whose sum is σ = 26366832. Its totient is φ = 17807328.

The previous prime is 21720649. The next prime is 21720689. The reversal of 21720671 is 17602712.

It is not a de Polignac number, because 21720671 - 2¹⁰ = 21719647 is a prime.

It is a plaindrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 21720671.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720631) 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, 8510 + ... + 10763.

It is an arithmetic number, because the mean of its divisors is an integer number (2197236).

Almost surely, 2^21720671 is an apocalyptic number.

21720671 is a deficient number, since it is larger than the sum of its proper divisors (4646161).

21720671 is a wasteful number, since it uses less digits than its factorization.

21720671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19310 (or 19303 counting only the distinct ones).

The product of its (nonzero) digits is 1176, while the sum is 26.

The square root of 21720671 is about 4660.5440669518. The cubic root of 21720671 is about 279.0129831276.

The spelling of 21720671 in words is "twenty-one million, seven hundred twenty thousand, six hundred seventy-one".