21105665651 has 8 divisors (see below), whose sum is σ = 25169489664. Its totient is φ = 17304023880.

The previous prime is 21105665639. The next prime is 21105665657. The reversal of 21105665651 is 15656650112.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21105665651 - 2³⁴ = 3925796467 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21105665657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 65545385 + ... + 65545706.

It is an arithmetic number, because the mean of its divisors is an integer number (3146186208).

Almost surely, 2^21105665651 is an apocalyptic number.

21105665651 is a deficient number, since it is larger than the sum of its proper divisors (4063824013).

21105665651 is a wasteful number, since it uses less digits than its factorization.

21105665651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 131091121.

The product of its (nonzero) digits is 54000, while the sum is 38.

The spelling of 21105665651 in words is "twenty-one billion, one hundred five million, six hundred sixty-five thousand, six hundred fifty-one".