21005511066551 has 16 divisors (see below), whose sum is σ = 24125195433600. Its totient is φ = 18087844975200.

The previous prime is 21005511066541. The next prime is 21005511066587. The reversal of 21005511066551 is 15566011550012.

It is not a de Polignac number, because 21005511066551 - 2¹⁸ = 21005510804407 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005511066541) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7151981 + ... + 9652038.

It is an arithmetic number, because the mean of its divisors is an integer number (1507824714600).

Almost surely, 2^{21005511066551} is an apocalyptic number.

21005511066551 is a deficient number, since it is larger than the sum of its proper divisors (3119684367049).

21005511066551 is a wasteful number, since it uses less digits than its factorization.

21005511066551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16810030.

The product of its (nonzero) digits is 45000, while the sum is 38.

The spelling of 21005511066551 in words is "twenty-one trillion, five billion, five hundred eleven million, sixty-six thousand, five hundred fifty-one".