1991390625 has 189 divisors, whose sum is σ = 4443048597. Its totient is φ = 856800000.

The previous prime is 1991390563. The next prime is 1991390629. The reversal of 1991390625 is 5260931991.

It is a happy number.

The square root of 1991390625 is 44625.

It is a perfect power (a square), and thus also a powerful number.

1991390625 is a `hidden beast` number, since 1 + 9 + 9 + 13 + 9 + 0 + 625 = 666.

It can be written as a sum of positive squares in 10 ways, for example, as 1957797009 + 33593616 = 44247^2 + 5796^2 .

It is not a de Polignac number, because 1991390625 - 2⁷ = 1991390497 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is not an unprimeable number, because it can be changed into a prime (1991390629) by changing a digit.

It is a polite number, since it can be written in 188 ways as a sum of consecutive naturals, for example, 117140617 + ... + 117140633.

Almost surely, 2^1991390625 is an apocalyptic number.

1991390625 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1991390625 is the 44625-th square number.

1991390625 is the 22313-rd centered octagonal number.

It is an amenable number.

1991390625 is an abundant number, since it is smaller than the sum of its proper divisors (2451657972).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1991390625 is an frugal number, since it uses more digits than its factorization.

1991390625 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84 (or 32 counting only the distinct ones).

The product of its (nonzero) digits is 131220, while the sum is 45.

The cubic root of 1991390625 is about 1258.1105941242.

The spelling of 1991390625 in words is "one billion, nine hundred ninety-one million, three hundred ninety thousand, six hundred twenty-five".