21081737521 has 8 divisors (see below), whose sum is σ = 22837751720. Its totient is φ = 19460063376.

The previous prime is 21081737513. The next prime is 21081737563. The reversal of 21081737521 is 12573718012.

It can be written as a sum of positive squares in 4 ways, for example, as 3307515121 + 17774222400 = 57511^2 + 133320^2 .

It is not a de Polignac number, because 21081737521 - 2³ = 21081737513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21081737221) 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, 4795650 + ... + 4800043.

It is an arithmetic number, because the mean of its divisors is an integer number (2854718965).

Almost surely, 2^21081737521 is an apocalyptic number.

It is an amenable number.

21081737521 is a deficient number, since it is larger than the sum of its proper divisors (1756014199).

21081737521 is an frugal number, since it uses more digits than its factorization.

21081737521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9595732 (or 9595706 counting only the distinct ones).

The product of its (nonzero) digits is 23520, while the sum is 37.

The spelling of 21081737521 in words is "twenty-one billion, eighty-one million, seven hundred thirty-seven thousand, five hundred twenty-one".