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  2. 1 + 2 + 3 + 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    The partial sums of the series 1 + 2 + 3 + 4 + 5 + 6 + ⋯ are 1, 3, 6, 10, 15, etc.The nth partial sum is given by a simple formula: = = (+). This equation was known ...

  3. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    For any integer n, n ≡ 1 (mod 2) if and only if 3n + 1 ≡ 4 (mod 6). Equivalently, ⁠ n − 1 / 3 ⁠ ≡ 1 (mod 2) if and only if n ≡ 4 (mod 6). Conjecturally, this inverse relation forms a tree except for the 12–4 loop (the inverse of the 4–21 loop of the unaltered function f defined in the Statement of the problem section of ...

  4. 1 − 2 + 3 − 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%E2%88%92_2_%2B_3_%E2%88...

    The idea becomes clearer by considering the general series 1 − 2x + 3x 2 − 4x 3 + 5x 4 − 6x 5 + &c. that arises while expanding the expression 1 ⁄ (1+x) 2, which this series is indeed equal to after we set x = 1.

  5. Harmonic series (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Harmonic_series_(mathematics)

    [3] The divergence of the harmonic series was first proven in 1350 by Nicole Oresme. [2] [4] Oresme's work, and the contemporaneous work of Richard Swineshead on a different series, marked the first appearance of infinite series other than the geometric series in mathematics. [5] However, this achievement fell into obscurity. [6]

  6. Four fours - Wikipedia

    en.wikipedia.org/wiki/Four_fours

    For example, when d=4, the hash table for two occurrences of d would contain the key-value pair 8 and 4+4, and the one for three occurrences, the key-value pair 2 and (4+4)/4 (strings shown in bold). The task is then reduced to recursively computing these hash tables for increasing n , starting from n=1 and continuing up to e.g. n=4.

  7. Boy or girl paradox - Wikipedia

    en.wikipedia.org/wiki/Boy_or_Girl_paradox

    Gardner initially gave the answers1 / 2 ⁠ and ⁠ 1 / 3 ⁠, respectively, but later acknowledged that the second question was ambiguous. Its answer could be ⁠ 1 / 2 ⁠ , depending on the procedure by which the information "at least one of them is a boy" was obtained.

  8. 2,2,4-Trimethylpentane - Wikipedia

    en.wikipedia.org/wiki/2,2,4-Trimethylpentane

    2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH 3) 3 CCH 2 CH (CH 3) 2. It is one of several isomers of octane (C 8 H 18 ). This particular isomer is the standard 100 point on the octane rating scale (the zero point is n -heptane ).

  9. Suggestions for optimal PRRs have varied from 3:1 (Shores, Gunter, & Jack, 1993), to 4:1 (Trussell, 2008), to 5:1 (Flora, 2000). A 3:1 ratio is often recommended for general education classrooms, but students with EBD may need higher ratios to improve their behavior (Rathel et al., 2014). As noted in previous work (Downs et al., 2018;