21721930 has 16 divisors (see below), whose sum is σ = 39572064. Its totient is φ = 8583760.

The previous prime is 21721927. The next prime is 21721933. The reversal of 21721930 is 3912712.

It is an interprime number because it is at equal distance from previous prime (21721927) and next prime (21721933).

It is a junction number, because it is equal to n+sod(n) for n = 21721895 and 21721904.

It is not an unprimeable number, because it can be changed into a prime (21721933) 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 7 ways as a sum of consecutive naturals, for example, 12256 + ... + 13915.

It is an arithmetic number, because the mean of its divisors is an integer number (2473254).

Almost surely, 2^21721930 is an apocalyptic number.

21721930 is a deficient number, since it is larger than the sum of its proper divisors (17850134).

21721930 is a wasteful number, since it uses less digits than its factorization.

21721930 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26261.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21721930 is about 4660.6791350618. The cubic root of 21721930 is about 279.0183738536.

It can be divided in two parts, 2172 and 1930, that multiplied together give a triangular number (4191960 = T₂₈₉₅).

The spelling of 21721930 in words is "twenty-one million, seven hundred twenty-one thousand, nine hundred thirty".