21631573 has 2 divisors, whose sum is σ = 21631574. Its totient is φ = 21631572.

The previous prime is 21631541. The next prime is 21631591. The reversal of 21631573 is 37513612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19342404 + 2289169 = 4398^2 + 1513^2 .

It is a cyclic number.

It is not a de Polignac number, because 21631573 - 2⁵ = 21631541 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21631513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815786 + 10815787.

It is an arithmetic number, because the mean of its divisors is an integer number (10815787).

Almost surely, 2^21631573 is an apocalyptic number.

It is an amenable number.

21631573 is a deficient number, since it is larger than the sum of its proper divisors (1).

21631573 is an equidigital number, since it uses as much as digits as its factorization.

21631573 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3780, while the sum is 28.

The square root of 21631573 is about 4650.9754890775. The cubic root of 21631573 is about 278.6309573668.

The spelling of 21631573 in words is "twenty-one million, six hundred thirty-one thousand, five hundred seventy-three".