21623778 has 24 divisors (see below), whose sum is σ = 51111216. Its totient is φ = 6552600.

The previous prime is 21623773. The next prime is 21623803. The reversal of 21623778 is 87732612.

21623778 is a `hidden beast` number, since 21 + 623 + 7 + 7 + 8 = 666.

It is a super-3 number, since 3×21623778³ (a number of 23 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21623773) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 54408 + ... + 54803.

It is an arithmetic number, because the mean of its divisors is an integer number (2129634).

Almost surely, 2^21623778 is an apocalyptic number.

21623778 is an abundant number, since it is smaller than the sum of its proper divisors (29487438).

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

21623778 is a wasteful number, since it uses less digits than its factorization.

21623778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109230 (or 109227 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21623778 is about 4650.1374173244. The cubic root of 21623778 is about 278.5974848549.

The spelling of 21623778 in words is "twenty-one million, six hundred twenty-three thousand, seven hundred seventy-eight".