21021606 has 20 divisors (see below), whose sum is σ = 47104332. Its totient is φ = 7007148.

The previous prime is 21021601. The next prime is 21021617. The reversal of 21021606 is 60612012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021601) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 64720 + ... + 65043.

Almost surely, 2^21021606 is an apocalyptic number.

21021606 is an abundant number, since it is smaller than the sum of its proper divisors (26082726).

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

21021606 is a wasteful number, since it uses less digits than its factorization.

21021606 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129777 (or 129768 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21021606 is about 4584.9324967768. The cubic root of 21021606 is about 275.9870031687.

Adding to 21021606 its reverse (60612012), we get a palindrome (81633618).

The spelling of 21021606 in words is "twenty-one million, twenty-one thousand, six hundred six".