661213501 has 4 divisors (see below), whose sum is σ = 712076092. Its totient is φ = 610350912.

The previous prime is 661213457. The next prime is 661213517. The reversal of 661213501 is 105312166.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 73102500 + 588111001 = 8550^2 + 24251^2 .

It is a cyclic number.

It is not a de Polignac number, because 661213501 - 2⁷ = 661213373 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661213571) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 25431276 + ... + 25431301.

It is an arithmetic number, because the mean of its divisors is an integer number (178019023).

Almost surely, 2^661213501 is an apocalyptic number.

It is an amenable number.

661213501 is a deficient number, since it is larger than the sum of its proper divisors (50862591).

661213501 is a wasteful number, since it uses less digits than its factorization.

661213501 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50862590.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 661213501 is about 25714.0720423662. The cubic root of 661213501 is about 871.1920511441.

Adding to 661213501 its reverse (105312166), we get a palindrome (766525667).

The spelling of 661213501 in words is "six hundred sixty-one million, two hundred thirteen thousand, five hundred one".