21681534 has 16 divisors (see below), whose sum is σ = 49557888. Its totient is φ = 6194712.

The previous prime is 21681533. The next prime is 21681547. The reversal of 21681534 is 43518612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681533) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 258072 + ... + 258155.

It is an arithmetic number, because the mean of its divisors is an integer number (3097368).

Almost surely, 2^21681534 is an apocalyptic number.

21681534 is an abundant number, since it is smaller than the sum of its proper divisors (27876354).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21681534 is a wasteful number, since it uses less digits than its factorization.

21681534 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 516239.

The product of its digits is 5760, while the sum is 30.

The square root of 21681534 is about 4656.3434151703. The cubic root of 21681534 is about 278.8453042040.

The spelling of 21681534 in words is "twenty-one million, six hundred eighty-one thousand, five hundred thirty-four".