661091623 has 2 divisors, whose sum is σ = 661091624. Its totient is φ = 661091622.

The previous prime is 661091621. The next prime is 661091677. The reversal of 661091623 is 326190166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661091623 - 2¹ = 661091621 is a prime.

Together with 661091621, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661091621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330545811 + 330545812.

It is an arithmetic number, because the mean of its divisors is an integer number (330545812).

Almost surely, 2^661091623 is an apocalyptic number.

661091623 is a deficient number, since it is larger than the sum of its proper divisors (1).

661091623 is an equidigital number, since it uses as much as digits as its factorization.

661091623 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 34.

The square root of 661091623 is about 25711.7020634574. The cubic root of 661091623 is about 871.1385204417.

The spelling of 661091623 in words is "six hundred sixty-one million, ninety-one thousand, six hundred twenty-three".