21661261615 has 16 divisors (see below), whose sum is σ = 30082913280. Its totient is φ = 14665416480.

The previous prime is 21661261591. The next prime is 21661261621. The reversal of 21661261615 is 51616216612.

It is not a de Polignac number, because 21661261615 - 2⁷ = 21661261487 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3914281 + ... + 3919810.

It is an arithmetic number, because the mean of its divisors is an integer number (1880182080).

Almost surely, 2^21661261615 is an apocalyptic number.

21661261615 is a deficient number, since it is larger than the sum of its proper divisors (8421651665).

21661261615 is an equidigital number, since it uses as much as digits as its factorization.

21661261615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7834182.

The product of its digits is 25920, while the sum is 37.

The spelling of 21661261615 in words is "twenty-one billion, six hundred sixty-one million, two hundred sixty-one thousand, six hundred fifteen".