21755720 has 32 divisors (see below), whose sum is σ = 55944000. Its totient is φ = 7459008.

The previous prime is 21755717. The next prime is 21755761. The reversal of 21755720 is 2755712.

It is a super-2 number, since 2×21755720² = 946622705436800, 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, 38570 + ... + 39129.

It is an arithmetic number, because the mean of its divisors is an integer number (1748250).

Almost surely, 2^21755720 is an apocalyptic number.

21755720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21755720 is an abundant number, since it is smaller than the sum of its proper divisors (34188280).

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

21755720 is a wasteful number, since it uses less digits than its factorization.

21755720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77717 (or 77713 counting only the distinct ones).

The product of its (nonzero) digits is 4900, while the sum is 29.

The square root of 21755720 is about 4664.3027346003. The cubic root of 21755720 is about 279.1629765112.

The spelling of 21755720 in words is "twenty-one million, seven hundred fifty-five thousand, seven hundred twenty".