21780387 has 16 divisors (see below), whose sum is σ = 32340000. Its totient is φ = 14487552.

The previous prime is 21780377. The next prime is 21780431. The reversal of 21780387 is 78308712.

It is not a de Polignac number, because 21780387 - 2¹⁶ = 21714851 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21780337) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 20239 + ... + 21287.

It is an arithmetic number, because the mean of its divisors is an integer number (2021250).

Almost surely, 2^21780387 is an apocalyptic number.

21780387 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21780387 is a deficient number, since it is larger than the sum of its proper divisors (10559613).

21780387 is a wasteful number, since it uses less digits than its factorization.

21780387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1827 (or 1821 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 36.

The square root of 21780387 is about 4666.9462178174. The cubic root of 21780387 is about 279.2684432153.

The spelling of 21780387 in words is "twenty-one million, seven hundred eighty thousand, three hundred eighty-seven".