21000527561 has 4 divisors (see below), whose sum is σ = 22615952772. Its totient is φ = 19385102352.

The previous prime is 21000527531. The next prime is 21000527579. The reversal of 21000527561 is 16572500012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9306267961 + 11694259600 = 96469^2 + 108140^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000527561 - 2¹⁰ = 21000526537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21000527521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 807712586 + ... + 807712611.

It is an arithmetic number, because the mean of its divisors is an integer number (5653988193).

Almost surely, 2^21000527561 is an apocalyptic number.

It is an amenable number.

21000527561 is a deficient number, since it is larger than the sum of its proper divisors (1615425211).

21000527561 is a wasteful number, since it uses less digits than its factorization.

21000527561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1615425210.

The product of its (nonzero) digits is 4200, while the sum is 29.

The spelling of 21000527561 in words is "twenty-one billion, five hundred twenty-seven thousand, five hundred sixty-one".