21521671 has 2 divisors, whose sum is σ = 21521672. Its totient is φ = 21521670.

The previous prime is 21521663. The next prime is 21521693. The reversal of 21521671 is 17612512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21521671 - 2³ = 21521663 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21521771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760835 + 10760836.

It is an arithmetic number, because the mean of its divisors is an integer number (10760836).

Almost surely, 2^21521671 is an apocalyptic number.

21521671 is a deficient number, since it is larger than the sum of its proper divisors (1).

21521671 is an equidigital number, since it uses as much as digits as its factorization.

21521671 is an evil number, because the sum of its binary digits is even.

The product of its digits is 840, while the sum is 25.

The square root of 21521671 is about 4639.1455032150. The cubic root of 21521671 is about 278.1582824455.

The spelling of 21521671 in words is "twenty-one million, five hundred twenty-one thousand, six hundred seventy-one".