21506731405665 has 48 divisors (see below), whose sum is σ = 39043518678528. Its totient is φ = 10091134944000.

The previous prime is 21506731405651. The next prime is 21506731405699. The reversal of 21506731405665 is 56650413760512.

It is a happy number.

It is not a de Polignac number, because 21506731405665 - 2¹⁵ = 21506731372897 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 191063716 + ... + 191176245.

It is an arithmetic number, because the mean of its divisors is an integer number (813406639136).

Almost surely, 2^{21506731405665} is an apocalyptic number.

It is an amenable number.

21506731405665 is a deficient number, since it is larger than the sum of its proper divisors (17536787272863).

21506731405665 is a wasteful number, since it uses less digits than its factorization.

21506731405665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 382240022 (or 382240011 counting only the distinct ones).

The product of its (nonzero) digits is 4536000, while the sum is 51.

The spelling of 21506731405665 in words is "twenty-one trillion, five hundred six billion, seven hundred thirty-one million, four hundred five thousand, six hundred sixty-five".