21661551161712 has 1600 divisors, whose sum is σ = 81280869120000. Its totient is φ = 5520397639680.

The previous prime is 21661551161687. The next prime is 21661551161713. The reversal of 21661551161712 is 21716115516612.

21661551161712 is a `hidden beast` number, since 2 + 1 + 6 + 6 + 1 + 5 + 5 + 11 + 617 + 12 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661551161713) by changing a digit.

It is a polite number, since it can be written in 319 ways as a sum of consecutive naturals, for example, 108852015789 + ... + 108852015987.

It is an arithmetic number, because the mean of its divisors is an integer number (50800543200).

Almost surely, 2^{21661551161712} is an apocalyptic number.

21661551161712 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21661551161712, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40640434560000).

21661551161712 is an abundant number, since it is smaller than the sum of its proper divisors (59619317958288).

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

21661551161712 is a wasteful number, since it uses less digits than its factorization.

21661551161712 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 561 (or 532 counting only the distinct ones).

The product of its digits is 151200, while the sum is 45.

The spelling of 21661551161712 in words is "twenty-one trillion, six hundred sixty-one billion, five hundred fifty-one million, one hundred sixty-one thousand, seven hundred twelve".