21721507 has 2 divisors, whose sum is σ = 21721508. Its totient is φ = 21721506.

The previous prime is 21721489. The next prime is 21721517. The reversal of 21721507 is 70512712.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21721507 - 2¹¹ = 21719459 is a prime.

It is not a weakly prime, because it can be changed into another 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 as a sum of consecutive naturals, namely, 10860753 + 10860754.

It is an arithmetic number, because the mean of its divisors is an integer number (10860754).

Almost surely, 2^21721507 is an apocalyptic number.

21721507 is a deficient number, since it is larger than the sum of its proper divisors (1).

21721507 is an equidigital number, since it uses as much as digits as its factorization.

21721507 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 980, while the sum is 25.

The square root of 21721507 is about 4660.6337551882. The cubic root of 21721507 is about 279.0165626957.

The spelling of 21721507 in words is "twenty-one million, seven hundred twenty-one thousand, five hundred seven".