661265003261 has 4 divisors (see below), whose sum is σ = 661901448000. Its totient is φ = 660628558524.

The previous prime is 661265003257. The next prime is 661265003263. The reversal of 661265003261 is 162300562166.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 162300562166 = 2 ⋅81150281083.

It is a cyclic number.

It is not a de Polignac number, because 661265003261 - 2² = 661265003257 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 (661265003263) 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, 318220811 + ... + 318222888.

It is an arithmetic number, because the mean of its divisors is an integer number (165475362000).

Almost surely, 2^661265003261 is an apocalyptic number.

It is an amenable number.

661265003261 is a deficient number, since it is larger than the sum of its proper divisors (636444739).

661265003261 is a wasteful number, since it uses less digits than its factorization.

661265003261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 636444738.

The product of its (nonzero) digits is 77760, while the sum is 38.

The spelling of 661265003261 in words is "six hundred sixty-one billion, two hundred sixty-five million, three thousand, two hundred sixty-one".