21723780 has 48 divisors (see below), whose sum is σ = 65507904. Its totient is φ = 5347200.

The previous prime is 21723763. The next prime is 21723791. The reversal of 21723780 is 8732712.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13146 + ... + 14705.

It is an arithmetic number, because the mean of its divisors is an integer number (1364748).

Almost surely, 2^21723780 is an apocalyptic number.

21723780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21723780 is an abundant number, since it is smaller than the sum of its proper divisors (43784124).

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

21723780 is a wasteful number, since it uses less digits than its factorization.

21723780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27876 (or 27874 counting only the distinct ones).

The product of its (nonzero) digits is 4704, while the sum is 30.

The square root of 21723780 is about 4660.8775997659. The cubic root of 21723780 is about 279.0262947173.

The spelling of 21723780 in words is "twenty-one million, seven hundred twenty-three thousand, seven hundred eighty".