Properties of the Number 661

Six Hundred Sixty-One

Basics

Value: 660 → 661 → 662

Parity: odd

Prime: Yes

Previous Prime: 659

Next Prime: 673

Digit Sum: 13

Digital Root: 4

Palindrome: No

Factorization: 661

Divisors: 1, 661

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1010010101

Octal: 1225

Duodecimal: 471

Hexadecimal: 295

Square: 436921

Square Root: 25.709920264364882

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Number of compositions of n such that no two adjacent parts are equal (these are sometimes called Carlitz compositions). A3242

Greater of twin primes. A6512

Primes with primitive root 2. A1122

Primes p such that 2p-1 is also prime. A5382

Primes congruent to 1 (mod 12). A68228

Primes p such that (p+1)/2 is prime. A5383

Primes of the form 10·n+1. A30430

Primes of the form 2x² + 13y². A107132

Centered 12-gonal numbers, or centered dodecagonal numbers: numbers of the form 6·k*(k-1) + 1. A3154

Primes whose base-2 representation is also the base-3 representation of a prime. A235266