21306137566 has 24 divisors (see below), whose sum is σ = 37274169600. Its totient is φ = 9107344512.

The previous prime is 21306137509. The next prime is 21306137579. The reversal of 21306137566 is 66573160312.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 246291 + ... + 321358.

It is an arithmetic number, because the mean of its divisors is an integer number (1553090400).

Almost surely, 2^21306137566 is an apocalyptic number.

21306137566 is a deficient number, since it is larger than the sum of its proper divisors (15968032034).

21306137566 is a wasteful number, since it uses less digits than its factorization.

21306137566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 568048 (or 568041 counting only the distinct ones).

The product of its (nonzero) digits is 136080, while the sum is 40.

Adding to 21306137566 its reverse (66573160312), we get a palindrome (87879297878).

The spelling of 21306137566 in words is "twenty-one billion, three hundred six million, one hundred thirty-seven thousand, five hundred sixty-six".