21163531501561 has 4 divisors (see below), whose sum is σ = 21179479906432. Its totient is φ = 21147583096692.

The previous prime is 21163531501549. The next prime is 21163531501579. The reversal of 21163531501561 is 16510513536112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21163531501561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21163531504561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7974200445 + ... + 7974203098.

It is an arithmetic number, because the mean of its divisors is an integer number (5294869976608).

Almost surely, 2^{21163531501561} is an apocalyptic number.

It is an amenable number.

21163531501561 is a deficient number, since it is larger than the sum of its proper divisors (15948404871).

21163531501561 is a wasteful number, since it uses less digits than its factorization.

21163531501561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15948404870.

The product of its (nonzero) digits is 81000, while the sum is 40.

The spelling of 21163531501561 in words is "twenty-one trillion, one hundred sixty-three billion, five hundred thirty-one million, five hundred one thousand, five hundred sixty-one".