1561749921 has 12 divisors (see below), whose sum is σ = 2256211620. Its totient is φ = 1041004800.

The previous prime is 1561749919. The next prime is 1561749923. The reversal of 1561749921 is 1299471651.

1561749921 is a `hidden beast` number, since 1 + 5 + 617 + 4 + 9 + 9 + 21 = 666.

It is an interprime number because it is at equal distance from previous prime (1561749919) and next prime (1561749923).

It can be written as a sum of positive squares in 2 ways, for example, as 938748321 + 623001600 = 30639^2 + 24960^2 .

It is not a de Polignac number, because 1561749921 - 2¹ = 1561749919 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1561749923) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 87225 + ... + 103593.

It is an arithmetic number, because the mean of its divisors is an integer number (188017635).

Almost surely, 2^1561749921 is an apocalyptic number.

It is an amenable number.

1561749921 is a deficient number, since it is larger than the sum of its proper divisors (694461699).

1561749921 is a wasteful number, since it uses less digits than its factorization.

1561749921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26976 (or 26973 counting only the distinct ones).

The product of its digits is 136080, while the sum is 45.

The square root of 1561749921 is about 39518.9817809113. The cubic root of 1561749921 is about 1160.2114955729.

The spelling of 1561749921 in words is "one billion, five hundred sixty-one million, seven hundred forty-nine thousand, nine hundred twenty-one".