21661145693 has 6 divisors (see below), whose sum is σ = 23809358622. Its totient is φ = 19691950520.

The previous prime is 21661145687. The next prime is 21661145713. The reversal of 21661145693 is 39654116612.

It can be written as a sum of positive squares in only one way, i.e., 16329517369 + 5331628324 = 127787^2 + 73018^2 .

It is not a de Polignac number, because 21661145693 - 2¹⁰ = 21661144669 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661145603) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 89508746 + ... + 89508987.

It is an arithmetic number, because the mean of its divisors is an integer number (3968226437).

Almost surely, 2^21661145693 is an apocalyptic number.

It is an amenable number.

21661145693 is a deficient number, since it is larger than the sum of its proper divisors (2148212929).

21661145693 is a wasteful number, since it uses less digits than its factorization.

21661145693 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179017755 (or 179017744 counting only the distinct ones).

The product of its digits is 233280, while the sum is 44.

The spelling of 21661145693 in words is "twenty-one billion, six hundred sixty-one million, one hundred forty-five thousand, six hundred ninety-three".