661323621 has 16 divisors (see below), whose sum is σ = 1008111104. Its totient is φ = 377756784.

The previous prime is 661323599. The next prime is 661323643. The reversal of 661323621 is 126323166.

It is an interprime number because it is at equal distance from previous prime (661323599) and next prime (661323643).

It is not a de Polignac number, because 661323621 - 2⁷ = 661323493 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661321621) 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, 80130 + ... + 87996.

It is an arithmetic number, because the mean of its divisors is an integer number (63006944).

Almost surely, 2^661323621 is an apocalyptic number.

It is an amenable number.

661323621 is a deficient number, since it is larger than the sum of its proper divisors (346787483).

661323621 is a wasteful number, since it uses less digits than its factorization.

661323621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11880.

The product of its digits is 7776, while the sum is 30.

The square root of 661323621 is about 25716.2131932367. The cubic root of 661323621 is about 871.2404118945.

Adding to 661323621 its reverse (126323166), we get a palindrome (787646787).

The spelling of 661323621 in words is "six hundred sixty-one million, three hundred twenty-three thousand, six hundred twenty-one".