999981551 has 2 divisors, whose sum is σ = 999981552. Its totient is φ = 999981550.

The previous prime is 999981547. The next prime is 999981607. The reversal of 999981551 is 155189999.

It is a happy number.

It is an a-pointer prime, because the next prime (999981607) can be obtained adding 999981551 to its sum of digits (56).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 999981551 - 2² = 999981547 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999921551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499990775 + 499990776.

It is an arithmetic number, because the mean of its divisors is an integer number (499990776).

Almost surely, 2^999981551 is an apocalyptic number.

999981551 is a deficient number, since it is larger than the sum of its proper divisors (1).

999981551 is an equidigital number, since it uses as much as digits as its factorization.

999981551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1312200, while the sum is 56.

The square root of 999981551 is about 31622.4848960356. The cubic root of 999981551 is about 999.9938502955.

The spelling of 999981551 in words is "nine hundred ninety-nine million, nine hundred eighty-one thousand, five hundred fifty-one".