21506205777571 has 16 divisors (see below), whose sum is σ = 22424062123008. Its totient is φ = 20610350208000.

The previous prime is 21506205777569. The next prime is 21506205777593. The reversal of 21506205777571 is 17577750260512.

It is a cyclic number.

It is not a de Polignac number, because 21506205777571 - 2¹ = 21506205777569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21506205777971) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19920870 + ... + 20972683.

It is an arithmetic number, because the mean of its divisors is an integer number (1401503882688).

Almost surely, 2^{21506205777571} is an apocalyptic number.

21506205777571 is a deficient number, since it is larger than the sum of its proper divisors (917856345437).

21506205777571 is a wasteful number, since it uses less digits than its factorization.

21506205777571 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40893822.

The product of its (nonzero) digits is 7203000, while the sum is 55.

The spelling of 21506205777571 in words is "twenty-one trillion, five hundred six billion, two hundred five million, seven hundred seventy-seven thousand, five hundred seventy-one".