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A070261 4th diagonal of triangle defined in A051537. 2
4, 10, 2, 28, 40, 6, 70, 88, 12, 130, 154, 20, 208, 238, 30, 304, 340, 42, 418, 460, 56, 550, 598, 72, 700, 754, 90, 868, 928, 110, 1054, 1120, 132, 1258, 1330, 156, 1480, 1558, 182, 1720, 1804, 210, 1978, 2068, 240, 2254, 2350, 272, 2548, 2650, 306, 2860 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = lcm(n + 3, n) / gcd(n + 3, n).
From Colin Barker, Mar 27 2017: (Start)
G.f.: 2*x*(2 + 5*x + x^2 + 8*x^3 + 5*x^4 - x^6 - x^7) / ((1 - x)^3*(1 + x + x^2)^3).
a(n) = 3*a(n-3) - 3*a(n-6) + a(n-9) for n>9.
(End)
From Amiram Eldar, Oct 08 2023: (Start)
Sum_{n>=1} 1/a(n) = 3/2.
Sum_{n>=1} (-1)^n/a(n) = 22*log(2)/9 - 7/6.
Sum_{k=1..n} a(k) ~ (19/81) * n^3. (End)
MATHEMATICA
Table[ LCM[i + 3, i] / GCD[i + 3, i], {i, 1, 60}]
PROG
(PARI) Vec(2*x*(2 + 5*x + x^2 + 8*x^3 + 5*x^4 - x^6 - x^7) / ((1 - x)^3*(1 + x + x^2)^3) + O(x^60)) \\ Colin Barker, Mar 27 2017
CROSSREFS
Cf. A051537.
Sequence in context: A337840 A349305 A244152 * A367029 A054048 A121512
KEYWORD
nonn,easy
AUTHOR
Amarnath Murthy, May 09 2002
EXTENSIONS
Edited by Robert G. Wilson v, May 10 2002
STATUS
approved

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Last modified June 20 08:30 EDT 2024. Contains 373512 sequences. (Running on oeis4.)