261921721005 has 144 divisors (see below), whose sum is σ = 538610776704. Its totient is φ = 117370632960.

The previous prime is 261921720989. The next prime is 261921721049. The reversal of 261921721005 is 500127129162.

261921721005 is a `hidden beast` number, since 2 + 619 + 2 + 17 + 21 + 0 + 0 + 5 = 666.

It is not a de Polignac number, because 261921721005 - 2⁴ = 261921720989 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 41289864 + ... + 41296206.

It is an arithmetic number, because the mean of its divisors is an integer number (3740352616).

Almost surely, 2^261921721005 is an apocalyptic number.

It is an amenable number.

261921721005 is an abundant number, since it is smaller than the sum of its proper divisors (276689055699).

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

261921721005 is a wasteful number, since it uses less digits than its factorization.

261921721005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6736 (or 6726 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 36.

The spelling of 261921721005 in words is "two hundred sixty-one billion, nine hundred twenty-one million, seven hundred twenty-one thousand, five".