661951 has 2 divisors, whose sum is σ = 661952. Its totient is φ = 661950.

The previous prime is 661949. The next prime is 661961. The reversal of 661951 is 159166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661951 - 2¹ = 661949 is a prime.

Together with 661949, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330975 + 330976.

It is an arithmetic number, because the mean of its divisors is an integer number (330976).

2⁶⁶¹⁹⁵¹ is an apocalyptic number.

661951 is a deficient number, since it is larger than the sum of its proper divisors (1).

661951 is an equidigital number, since it uses as much as digits as its factorization.

661951 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1620, while the sum is 28.

The square root of 661951 is about 813.6037118893. The cubic root of 661951 is about 87.1515831858.

It can be divided in two parts, 6619 and 51, that added together give a triangular number (6670 = T₁₁₅).

The spelling of 661951 in words is "six hundred sixty-one thousand, nine hundred fifty-one".