661555506651 has 16 divisors (see below), whose sum is σ = 1005803848224. Its totient is φ = 383163369984.

The previous prime is 661555506643. The next prime is 661555506779. The reversal of 661555506651 is 156605555166.

It is not a de Polignac number, because 661555506651 - 2³ = 661555506643 is a prime.

It is a super-2 number, since 2×661555506651² (a number of 24 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (51).

It is a junction number, because it is equal to n+sod(n) for n = 661555506594 and 661555506603.

It is not an unprimeable number, because it can be changed into a prime (661555502651) 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, 498909976 + ... + 498911301.

It is an arithmetic number, because the mean of its divisors is an integer number (62862740514).

Almost surely, 2^661555506651 is an apocalyptic number.

661555506651 is a deficient number, since it is larger than the sum of its proper divisors (344248341573).

661555506651 is a wasteful number, since it uses less digits than its factorization.

661555506651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 997821310.

The product of its (nonzero) digits is 4050000, while the sum is 51.

The spelling of 661555506651 in words is "six hundred sixty-one billion, five hundred fifty-five million, five hundred six thousand, six hundred fifty-one".