21721431 has 8 divisors (see below), whose sum is σ = 29668464. Its totient is φ = 14127680.

The previous prime is 21721409. The next prime is 21721457. The reversal of 21721431 is 13412712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21721431 - 2⁷ = 21721303 is a prime.

It is a super-2 number, since 2×21721431² = 943641129375522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21721398 and 21721407.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721031) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 88176 + ... + 88421.

It is an arithmetic number, because the mean of its divisors is an integer number (3708558).

Almost surely, 2^21721431 is an apocalyptic number.

21721431 is a deficient number, since it is larger than the sum of its proper divisors (7947033).

21721431 is a wasteful number, since it uses less digits than its factorization.

21721431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176641.

The product of its digits is 336, while the sum is 21.

The square root of 21721431 is about 4660.6256017835. The cubic root of 21721431 is about 279.0162372842.

The spelling of 21721431 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred thirty-one".