661261637 has 4 divisors (see below), whose sum is σ = 661470156. Its totient is φ = 661053120.

The previous prime is 661261633. The next prime is 661261639. The reversal of 661261637 is 736162166.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 519794401 + 141467236 = 22799^2 + 11894^2 .

It is a cyclic number.

It is not a de Polignac number, because 661261637 - 2² = 661261633 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661261637.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661261633) 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, 99428 + ... + 105869.

It is an arithmetic number, because the mean of its divisors is an integer number (165367539).

Almost surely, 2^661261637 is an apocalyptic number.

It is an amenable number.

661261637 is a deficient number, since it is larger than the sum of its proper divisors (208519).

661261637 is a wasteful number, since it uses less digits than its factorization.

661261637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 208518.

The product of its digits is 54432, while the sum is 38.

The square root of 661261637 is about 25715.0080108873. The cubic root of 661261637 is about 871.2131914076.

The spelling of 661261637 in words is "six hundred sixty-one million, two hundred sixty-one thousand, six hundred thirty-seven".