21961557 has 32 divisors (see below), whose sum is σ = 33696000. Its totient is φ = 14129856.

The previous prime is 21961543. The next prime is 21961561. The reversal of 21961557 is 75516912.

It is a de Polignac number, because none of the positive numbers 2^k-21961557 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21961517) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 147319 + ... + 147467.

It is an arithmetic number, because the mean of its divisors is an integer number (1053000).

Almost surely, 2^21961557 is an apocalyptic number.

21961557 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21961557 is a deficient number, since it is larger than the sum of its proper divisors (11734443).

21961557 is a wasteful number, since it uses less digits than its factorization.

21961557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 314 (or 308 counting only the distinct ones).

The product of its digits is 18900, while the sum is 36.

The square root of 21961557 is about 4686.3159304511. The cubic root of 21961557 is about 280.0406276081.

It can be divided in two parts, 219 and 61557, that added together give a triangular number (61776 = T₃₅₁).

The spelling of 21961557 in words is "twenty-one million, nine hundred sixty-one thousand, five hundred fifty-seven".