21661640744655 has 32 divisors (see below), whose sum is σ = 35471756415744. Its totient is φ = 11281939151616.

The previous prime is 21661640744591. The next prime is 21661640744729. The reversal of 21661640744655 is 55644704616612.

It is not a de Polignac number, because 21661640744655 - 2⁶ = 21661640744591 is a prime.

It is a super-2 number, since 2×21661640744655² (a number of 27 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21661640744595 and 21661640744604.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 150534 + ... + 6583763.

It is an arithmetic number, because the mean of its divisors is an integer number (1108492387992).

Almost surely, 2^{21661640744655} is an apocalyptic number.

21661640744655 is a deficient number, since it is larger than the sum of its proper divisors (13810115671089).

21661640744655 is a wasteful number, since it uses less digits than its factorization.

21661640744655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6739335.

The product of its (nonzero) digits is 29030400, while the sum is 57.

The spelling of 21661640744655 in words is "twenty-one trillion, six hundred sixty-one billion, six hundred forty million, seven hundred forty-four thousand, six hundred fifty-five".