661505600551 has 4 divisors (see below), whose sum is σ = 661507238952. Its totient is φ = 661503962152.

The previous prime is 661505600543. The next prime is 661505600557. The reversal of 661505600551 is 155006505166.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 661505600551 - 2³ = 661505600543 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 (661505600557) 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, 262761 + ... + 1179853.

It is an arithmetic number, because the mean of its divisors is an integer number (165376809738).

Almost surely, 2^661505600551 is an apocalyptic number.

661505600551 is a deficient number, since it is larger than the sum of its proper divisors (1638401).

661505600551 is an equidigital number, since it uses as much as digits as its factorization.

661505600551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1638400.

The product of its (nonzero) digits is 135000, while the sum is 40.

The spelling of 661505600551 in words is "six hundred sixty-one billion, five hundred five million, six hundred thousand, five hundred fifty-one".