21681071 has 4 divisors (see below), whose sum is σ = 22822200. Its totient is φ = 20539944.

The previous prime is 21681061. The next prime is 21681091. The reversal of 21681071 is 17018612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21681071 - 2⁶ = 21681007 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21681071.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681031) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 570536 + ... + 570573.

It is an arithmetic number, because the mean of its divisors is an integer number (5705550).

Almost surely, 2^21681071 is an apocalyptic number.

21681071 is a deficient number, since it is larger than the sum of its proper divisors (1141129).

21681071 is a wasteful number, since it uses less digits than its factorization.

21681071 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1141128.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 21681071 is about 4656.2936977815. The cubic root of 21681071 is about 278.8433193153.

Adding to 21681071 its reverse (17018612), we get a palindrome (38699683).

The spelling of 21681071 in words is "twenty-one million, six hundred eighty-one thousand, seventy-one".