661531105661 has 2 divisors, whose sum is σ = 661531105662. Its totient is φ = 661531105660.

The previous prime is 661531105643. The next prime is 661531105691. The reversal of 661531105661 is 166501135166.

661531105661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 468137850436 + 193393255225 = 684206^2 + 439765^2 .

It is a cyclic number.

It is not a de Polignac number, because 661531105661 - 2¹⁸ = 661530843517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661531105691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330765552830 + 330765552831.

It is an arithmetic number, because the mean of its divisors is an integer number (330765552831).

Almost surely, 2^661531105661 is an apocalyptic number.

It is an amenable number.

661531105661 is a deficient number, since it is larger than the sum of its proper divisors (1).

661531105661 is an equidigital number, since it uses as much as digits as its factorization.

661531105661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 97200, while the sum is 41.

The spelling of 661531105661 in words is "six hundred sixty-one billion, five hundred thirty-one million, one hundred five thousand, six hundred sixty-one".