Natural (counting) numbers: 1, 2, 3, 4, ... Whole numbers: 0, 1, 2, 3, ... Integers: ..., −3, −2, −1, 0, 1, 2, 3, ... Rational numbers: Numbers that can be written as a fraction of two integers Irrational numbers: Numbers that cannot be written as a fraction Real numbers: All rational and irrational numbers Imaginary numbers: Multiples of i, where i² = −1 Complex numbers: Numbers of the form a + bi Even numbers: Whole numbers divisible by 2 Odd numbers: Whole numbers not divisible by 2 Prime numbers: Numbers above 1 with exactly two factors Composite numbers: Numbers above 1 that are not prime Square numbers: 1, 4, 9, 16, 25, ... Cube numbers: 1, 8, 27, 64, 125, ... Triangular numbers: 1, 3, 6, 10, 15, 21, ... Fibonacci numbers: 1, 1, 2, 3, 5, 8, 13, 21, ... Perfect numbers: Numbers equal to the sum of their proper factors: 6, 28, 496 Is 6 perfect?: Yes: 1 + 2 + 3 = 6 Is 28 perfect?: Yes: 1 + 2 + 4 + 7 + 14 = 28 Palindromic number: A number that reads the same backward and forward Twin primes: Primes that differ by 2 Mersenne prime: A prime of the form 2ⁿ − 1 Pi is rational or irrational?: Irrational √2 is rational or irrational?: Irrational √9 is rational or irrational?: Rational (it equals 3) 0.5 is rational or irrational?: Rational 0.333... is rational or irrational?: Rational (1/3) Is e rational or irrational?: Irrational Is zero positive or negative?: Neither Is zero even?: Yes Is 1 prime?: No Is 0 an integer?: Yes Is −4 a whole number?: No Is −4 an integer?: Yes Is 3/4 an integer?: No, it is rational Is every integer a rational number?: Yes (n = n/1) Is every rational number an integer?: No Is every real number rational?: No Ordinal numbers: First, second, third: tell position Cardinal numbers: One, two, three: tell how many Nominal numbers: Numbers used as names or labels, like a jersey number Opposite of 7: −7 Reciprocal of 7: 1/7 Absolute value of −7: 7 Negative of a negative: A positive: −(−7) = 7 Googol: 10^100 Googolplex: 10 to the power of a googol Infinity: Not a number; the idea of going on without end Golden ratio: About 1.618, an irrational number: (1 + √5)/2 Free flashcards from Peabody at peabody.kids/flashcards/math-number-types