21721510 has 8 divisors (see below), whose sum is σ = 39098736. Its totient is φ = 8688600.

The previous prime is 21721507. The next prime is 21721517. The reversal of 21721510 is 1512712.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721517) 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 3 ways as a sum of consecutive naturals, for example, 1086066 + ... + 1086085.

It is an arithmetic number, because the mean of its divisors is an integer number (4887342).

Almost surely, 2^21721510 is an apocalyptic number.

21721510 is a deficient number, since it is larger than the sum of its proper divisors (17377226).

21721510 is a wasteful number, since it uses less digits than its factorization.

21721510 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2172158.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21721510 is about 4660.6340770329. The cubic root of 21721510 is about 279.0165755409.

The spelling of 21721510 in words is "twenty-one million, seven hundred twenty-one thousand, five hundred ten".