21129806 has 16 divisors (see below), whose sum is σ = 33121440. Its totient is φ = 10096800.

The previous prime is 21129803. The next prime is 21129809. The reversal of 21129806 is 60892112.

21129806 = T₆₅₃ + T₆₅₄ + ... + T₇₃₉.

It is an interprime number because it is at equal distance from previous prime (21129803) and next prime (21129809).

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21129803) 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 7 ways as a sum of consecutive naturals, for example, 4055 + ... + 7661.

It is an arithmetic number, because the mean of its divisors is an integer number (2070090).

Almost surely, 2^21129806 is an apocalyptic number.

21129806 is a deficient number, since it is larger than the sum of its proper divisors (11991634).

21129806 is a wasteful number, since it uses less digits than its factorization.

21129806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3739.

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 21129806 is about 4596.7168718554. The cubic root of 21129806 is about 276.4597026382.

The spelling of 21129806 in words is "twenty-one million, one hundred twenty-nine thousand, eight hundred six".