19991551 has 2 divisors, whose sum is σ = 19991552. Its totient is φ = 19991550.

The previous prime is 19991549. The next prime is 19991557. The reversal of 19991551 is 15519991.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 19991551 - 2¹ = 19991549 is a prime.

It is a super-2 number, since 2×19991551² = 799324222771202, which contains 22 as substring.

Together with 19991549, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19991557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9995775 + 9995776.

It is an arithmetic number, because the mean of its divisors is an integer number (9995776).

Almost surely, 2^19991551 is an apocalyptic number.

19991551 is a deficient number, since it is larger than the sum of its proper divisors (1).

19991551 is an equidigital number, since it uses as much as digits as its factorization.

19991551 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18225, while the sum is 40.

The square root of 19991551 is about 4471.1912282970. The cubic root of 19991551 is about 271.4035327516.

The spelling of 19991551 in words is "nineteen million, nine hundred ninety-one thousand, five hundred fifty-one".