261657136410721 has 4 divisors (see below), whose sum is σ = 261657363241152. Its totient is φ = 261656909580292.

The previous prime is 261657136410661. The next prime is 261657136410767. The reversal of 261657136410721 is 127014631756162.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 261657136410721 - 2¹⁵ = 261657136377953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261657136410421) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111676021 + ... + 113994946.

It is an arithmetic number, because the mean of its divisors is an integer number (65414340810288).

Almost surely, 2^{261657136410721} is an apocalyptic number.

It is an amenable number.

261657136410721 is a deficient number, since it is larger than the sum of its proper divisors (226830431).

261657136410721 is a wasteful number, since it uses less digits than its factorization.

261657136410721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 226830430.

The product of its (nonzero) digits is 2540160, while the sum is 52.

The spelling of 261657136410721 in words is "two hundred sixty-one trillion, six hundred fifty-seven billion, one hundred thirty-six million, four hundred ten thousand, seven hundred twenty-one".