19911661 has 32 divisors (see below), whose sum is σ = 26484480. Its totient is φ = 14515200.

The previous prime is 19911659. The next prime is 19911673. The reversal of 19911661 is 16611991.

19911661 = 138² + 139² + ... + 396².

It is not a de Polignac number, because 19911661 - 2¹ = 19911659 is a prime.

19911661 is a strobogrammatic number because it is the same when read upside-down.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19911631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 82501 + ... + 82741.

It is an arithmetic number, because the mean of its divisors is an integer number (827640).

Almost surely, 2^19911661 is an apocalyptic number.

19911661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

19911661 is a deficient number, since it is larger than the sum of its proper divisors (6572819).

19911661 is a wasteful number, since it uses less digits than its factorization.

19911661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 325.

The product of its digits is 2916, while the sum is 34.

The square root of 19911661 is about 4462.2484242812. The cubic root of 19911661 is about 271.0415235729.

The spelling of 19911661 in words is "nineteen million, nine hundred eleven thousand, six hundred sixty-one".