21001226724 has 135 divisors (see below), whose sum is σ = 56149587417. Its totient is φ = 6844766976.

The previous prime is 21001226713. The next prime is 21001226749. The reversal of 21001226724 is 42762210012.

The square root of 21001226724 is 144918.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 9430352100 + 11570874624 = 97110^2 + 107568^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 216507444 + ... + 216507540.

Almost surely, 2^21001226724 is an apocalyptic number.

21001226724 is the 144918-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001226724

21001226724 is an abundant number, since it is smaller than the sum of its proper divisors (35148360693).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21001226724 is an frugal number, since it uses more digits than its factorization.

21001226724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 376 (or 185 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

Adding to 21001226724 its reverse (42762210012), we get a palindrome (63763436736).

The spelling of 21001226724 in words is "twenty-one billion, one million, two hundred twenty-six thousand, seven hundred twenty-four".