21561401 has 2 divisors, whose sum is σ = 21561402. Its totient is φ = 21561400.

The previous prime is 21561383. The next prime is 21561427. The reversal of 21561401 is 10416512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18835600 + 2725801 = 4340^2 + 1651^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561401 - 2¹⁰ = 21560377 is a prime.

It is a Chen prime.

It is equal to p_1363223 and since 21561401 and 1363223 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21561481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780700 + 10780701.

It is an arithmetic number, because the mean of its divisors is an integer number (10780701).

Almost surely, 2^21561401 is an apocalyptic number.

It is an amenable number.

21561401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561401 is an equidigital number, since it uses as much as digits as its factorization.

21561401 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 21561401 is about 4643.4255674017. The cubic root of 21561401 is about 278.3293415788.

Adding to 21561401 its reverse (10416512), we get a palindrome (31977913).

It can be divided in two parts, 215 and 61401, that added together give a palindrome (61616).

The spelling of 21561401 in words is "twenty-one million, five hundred sixty-one thousand, four hundred one".