15561621 has 24 divisors (see below), whose sum is σ = 23104224. Its totient is φ = 10090080.

The previous prime is 15561619. The next prime is 15561631. The reversal of 15561621 is 12616551.

It is a happy number.

It is not a de Polignac number, because 15561621 - 2¹ = 15561619 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15561631) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 78895 + ... + 79091.

It is an arithmetic number, because the mean of its divisors is an integer number (962676).

Almost surely, 2^15561621 is an apocalyptic number.

It is an amenable number.

15561621 is a deficient number, since it is larger than the sum of its proper divisors (7542603).

15561621 is a wasteful number, since it uses less digits than its factorization.

15561621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 401 (or 398 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 15561621 is about 3944.8220492184. The cubic root of 15561621 is about 249.6615206003.

It can be divided in two parts, 155 and 61621, that added together give a triangular number (61776 = T₃₅₁).

The spelling of 15561621 in words is "fifteen million, five hundred sixty-one thousand, six hundred twenty-one".