1621561620 has 96 divisors (see below), whose sum is σ = 5207102208. Its totient is φ = 369349632.

The previous prime is 1621561607. The next prime is 1621561637. The reversal of 1621561620 is 261651261.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 116472 + ... + 129648.

It is an arithmetic number, because the mean of its divisors is an integer number (54240648).

Almost surely, 2^1621561620 is an apocalyptic number.

1621561620 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1621561620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2603551104).

1621561620 is an abundant number, since it is smaller than the sum of its proper divisors (3585540588).

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

1621561620 is a wasteful number, since it uses less digits than its factorization.

1621561620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13489 (or 13487 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 30.

The square root of 1621561620 is about 40268.6183025939. The cubic root of 1621561620 is about 1174.8375498969.

The spelling of 1621561620 in words is "one billion, six hundred twenty-one million, five hundred sixty-one thousand, six hundred twenty".