21771984 has 160 divisors (see below), whose sum is σ = 66495744. Its totient is φ = 6082560.

The previous prime is 21771983. The next prime is 21772001. The reversal of 21771984 is 48917712.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21771983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 531004 + ... + 531044.

Almost surely, 2^21771984 is an apocalyptic number.

21771984 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21771984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33247872).

21771984 is an abundant number, since it is smaller than the sum of its proper divisors (44723760).

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

21771984 is a wasteful number, since it uses less digits than its factorization.

21771984 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125 (or 119 counting only the distinct ones).

The product of its digits is 28224, while the sum is 39.

The square root of 21771984 is about 4666.0458634694. The cubic root of 21771984 is about 279.2325241323.

The spelling of 21771984 in words is "twenty-one million, seven hundred seventy-one thousand, nine hundred eighty-four".