61991409 has 4 divisors (see below), whose sum is σ = 82655216. Its totient is φ = 41327604.

The previous prime is 61991399. The next prime is 61991411. The reversal of 61991409 is 90419916.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 61991409 - 2⁴ = 61991393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (61996409) 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, 10331899 + ... + 10331904.

It is an arithmetic number, because the mean of its divisors is an integer number (20663804).

Almost surely, 2^61991409 is an apocalyptic number.

It is an amenable number.

61991409 is a deficient number, since it is larger than the sum of its proper divisors (20663807).

61991409 is a wasteful number, since it uses less digits than its factorization.

61991409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20663806.

The product of its (nonzero) digits is 17496, while the sum is 39.

The square root of 61991409 is about 7873.4623260672. The cubic root of 61991409 is about 395.7708793458.

The spelling of 61991409 in words is "sixty-one million, nine hundred ninety-one thousand, four hundred nine".