2661243065261 has 6 divisors (see below), whose sum is σ = 2925167997486. Its totient is φ = 2419311877400.

The previous prime is 2661243065209. The next prime is 2661243065309. The reversal of 2661243065261 is 1625603421662.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 2097138422500 + 564104642761 = 1448150^2 + 751069^2 .

It is a de Polignac number, because none of the positive numbers 2^k-2661243065261 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2661243065161) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 10996872050 + ... + 10996872291.

It is an arithmetic number, because the mean of its divisors is an integer number (487527999581).

Almost surely, 2^{2661243065261} is an apocalyptic number.

It is an amenable number.

2661243065261 is a deficient number, since it is larger than the sum of its proper divisors (263924932225).

2661243065261 is a wasteful number, since it uses less digits than its factorization.

2661243065261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21993744363 (or 21993744352 counting only the distinct ones).

The product of its (nonzero) digits is 622080, while the sum is 44.

The spelling of 2661243065261 in words is "two trillion, six hundred sixty-one billion, two hundred forty-three million, sixty-five thousand, two hundred sixty-one".