21666077561656 has 64 divisors (see below), whose sum is σ = 44564374632960. Its totient is φ = 9793246032000.

The previous prime is 21666077561593. The next prime is 21666077561657. The reversal of 21666077561656 is 65616577066612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666077561657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 420584941 + ... + 420636451.

It is an arithmetic number, because the mean of its divisors is an integer number (696318353640).

Almost surely, 2^{21666077561656} is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21666077561656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22282187316480).

21666077561656 is an abundant number, since it is smaller than the sum of its proper divisors (22898297071304).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21666077561656 is a wasteful number, since it uses less digits than its factorization.

21666077561656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78116 (or 78112 counting only the distinct ones).

The product of its (nonzero) digits is 114307200, while the sum is 64.

The spelling of 21666077561656 in words is "twenty-one trillion, six hundred sixty-six billion, seventy-seven million, five hundred sixty-one thousand, six hundred fifty-six".