661415621 has 2 divisors, whose sum is σ = 661415622. Its totient is φ = 661415620.

The previous prime is 661415591. The next prime is 661415639. The reversal of 661415621 is 126514166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 409050625 + 252364996 = 20225^2 + 15886^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661415621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661415681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330707810 + 330707811.

It is an arithmetic number, because the mean of its divisors is an integer number (330707811).

Almost surely, 2^661415621 is an apocalyptic number.

It is an amenable number.

661415621 is a deficient number, since it is larger than the sum of its proper divisors (1).

661415621 is an equidigital number, since it uses as much as digits as its factorization.

661415621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 32.

The square root of 661415621 is about 25718.0018858386. The cubic root of 661415621 is about 871.2808108756.

Adding to 661415621 its reverse (126514166), we get a palindrome (787929787).

The spelling of 661415621 in words is "six hundred sixty-one million, four hundred fifteen thousand, six hundred twenty-one".