21643671 has 16 divisors (see below), whose sum is σ = 33225984. Its totient is φ = 12275904.

The previous prime is 21643607. The next prime is 21643691. The reversal of 21643671 is 17634612.

It is not a de Polignac number, because 21643671 - 2⁶ = 21643607 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21643691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 885 + ... + 6638.

It is an arithmetic number, because the mean of its divisors is an integer number (2076624).

Almost surely, 2^21643671 is an apocalyptic number.

21643671 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21643671 is a deficient number, since it is larger than the sum of its proper divisors (11582313).

21643671 is a wasteful number, since it uses less digits than its factorization.

21643671 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7670.

The product of its digits is 6048, while the sum is 30.

The square root of 21643671 is about 4652.2758946563. The cubic root of 21643671 is about 278.6828914710.

The spelling of 21643671 in words is "twenty-one million, six hundred forty-three thousand, six hundred seventy-one".