21685640505 has 16 divisors (see below), whose sum is σ = 36205591680. Its totient is φ = 11062819328.

The previous prime is 21685640489. The next prime is 21685640513. The reversal of 21685640505 is 50504658612.

It is a cyclic number.

It is not a de Polignac number, because 21685640505 - 2⁴ = 21685640489 is a prime.

It is a super-2 number, since 2×21685640505² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 31428120 + ... + 31428809.

It is an arithmetic number, because the mean of its divisors is an integer number (2262849480).

Almost surely, 2^21685640505 is an apocalyptic number.

It is an amenable number.

21685640505 is a deficient number, since it is larger than the sum of its proper divisors (14519951175).

21685640505 is a wasteful number, since it uses less digits than its factorization.

21685640505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62856960.

The product of its (nonzero) digits is 288000, while the sum is 42.

The spelling of 21685640505 in words is "twenty-one billion, six hundred eighty-five million, six hundred forty thousand, five hundred five".