33991561 has 4 divisors (see below), whose sum is σ = 34005712. Its totient is φ = 33977412.

The previous prime is 33991547. The next prime is 33991597. The reversal of 33991561 is 16519933.

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, and also an emirpimes, since its reverse is a distinct semiprime: 16519933 = 233 ⋅70901.

It is a cyclic number.

It is not a de Polignac number, because 33991561 - 2²¹ = 31894409 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 33991561.

It is not an unprimeable number, because it can be changed into a prime (33991511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2475 + ... + 8608.

It is an arithmetic number, because the mean of its divisors is an integer number (8501428).

Almost surely, 2^33991561 is an apocalyptic number.

It is an amenable number.

33991561 is a deficient number, since it is larger than the sum of its proper divisors (14151).

33991561 is a wasteful number, since it uses less digits than its factorization.

33991561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14150.

The product of its digits is 21870, while the sum is 37.

The square root of 33991561 is about 5830.2282116569. The cubic root of 33991561 is about 323.9343748864.

The spelling of 33991561 in words is "thirty-three million, nine hundred ninety-one thousand, five hundred sixty-one".