21691980 has 36 divisors (see below), whose sum is σ = 65799552. Its totient is φ = 5784480.

The previous prime is 21691979. The next prime is 21692063. The reversal of 21691980 is 8919612.

It is a tau number, because it is divible by the number of its divisors (36).

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

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 60076 + ... + 60435.

Almost surely, 2^21691980 is an apocalyptic number.

21691980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21691980 is an abundant number, since it is smaller than the sum of its proper divisors (44107572).

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

21691980 is a wasteful number, since it uses less digits than its factorization.

21691980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120526 (or 120521 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21691980 is about 4657.4649757137. The cubic root of 21691980 is about 278.8900788708.

The spelling of 21691980 in words is "twenty-one million, six hundred ninety-one thousand, nine hundred eighty".