21651816 has 32 divisors (see below), whose sum is σ = 54345600. Its totient is φ = 7188480.

The previous prime is 21651803. The next prime is 21651823. The reversal of 21651816 is 61815612.

It is a super-2 number, since 2×21651816² = 937602272195712, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4840 + ... + 8168.

It is an arithmetic number, because the mean of its divisors is an integer number (1698300).

Almost surely, 2^21651816 is an apocalyptic number.

It is an amenable number.

21651816 is an abundant number, since it is smaller than the sum of its proper divisors (32693784).

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

21651816 is a wasteful number, since it uses less digits than its factorization.

21651816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3609 (or 3605 counting only the distinct ones).

The product of its digits is 2880, while the sum is 30.

The square root of 21651816 is about 4653.1511903225. The cubic root of 21651816 is about 278.7178452993.

The spelling of 21651816 in words is "twenty-one million, six hundred fifty-one thousand, eight hundred sixteen".