21679740 has 72 divisors (see below), whose sum is σ = 67315248. Its totient is φ = 5644800.

The previous prime is 21679739. The next prime is 21679753. The reversal of 21679740 is 4797612.

It is a happy number.

It is a super-2 number, since 2×21679740² = 940022252935200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21679695 and 21679704.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6340 + ... + 9140.

It is an arithmetic number, because the mean of its divisors is an integer number (934934).

Almost surely, 2^21679740 is an apocalyptic number.

21679740 is a gapful number since it is divisible by the number (20) 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 21679740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33657624).

21679740 is an abundant number, since it is smaller than the sum of its proper divisors (45635508).

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

21679740 is a wasteful number, since it uses less digits than its factorization.

21679740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2859 (or 2854 counting only the distinct ones).

The product of its (nonzero) digits is 21168, while the sum is 36.

The square root of 21679740 is about 4656.1507707547. The cubic root of 21679740 is about 278.8376131388.

The spelling of 21679740 in words is "twenty-one million, six hundred seventy-nine thousand, seven hundred forty".