661131261 has 16 divisors (see below), whose sum is σ = 1119376000. Its totient is φ = 377789184.

The previous prime is 661131257. The next prime is 661131283. The reversal of 661131261 is 162131166.

It is not a de Polignac number, because 661131261 - 2² = 661131257 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661131061) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1748836 + ... + 1749213.

It is an arithmetic number, because the mean of its divisors is an integer number (69961000).

Almost surely, 2^661131261 is an apocalyptic number.

It is an amenable number.

661131261 is a deficient number, since it is larger than the sum of its proper divisors (458244739).

661131261 is a wasteful number, since it uses less digits than its factorization.

661131261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3498065 (or 3498059 counting only the distinct ones).

The product of its digits is 1296, while the sum is 27.

The square root of 661131261 is about 25712.4728682404. The cubic root of 661131261 is about 871.1559307862.

The spelling of 661131261 in words is "six hundred sixty-one million, one hundred thirty-one thousand, two hundred sixty-one".