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A134154
a(n) = 15*n^2 - 9*n + 1.
11
1, 7, 43, 109, 205, 331, 487, 673, 889, 1135, 1411, 1717, 2053, 2419, 2815, 3241, 3697, 4183, 4699, 5245, 5821, 6427, 7063, 7729, 8425, 9151, 9907, 10693, 11509, 12355, 13231, 14137, 15073, 16039, 17035, 18061, 19117, 20203, 21319, 22465, 23641
OFFSET
0,2
COMMENTS
A119617 is union of A134153 and A134154 A000538(n) is divisible by A000330(n) if and only n is congruent to {1, 3} mod 5 (see A047219) A134154(n) is case when n is congruent to 3 mod 5 see cases 2)
FORMULA
a(n) = 15*n^2 - 9*n + 1.
a(n+1) = (3*(5*n + 3)^2 + 3*(5*n + 3) - 1)/5.
a(n+1) = (Sum_{k=1..5*n+3} k^4) / (Sum_{k=1..5*n+3} k^2).
G.f.: -(1+4*x+25*x^2)/(-1+x)^3. - R. J. Mathar, Nov 14 2007
MATHEMATICA
1) Table[1 - 9 n + 15 n^2, {n, 0, 50}] 2) Table[Sum[k^4, {k, 1, 5m + 3}]/Sum[k^2, {k, 1, 5m + 3}], {m, 0, 30}] (*Artur Jasinski*)
PROG
(PARI) a(n)=15*n^2-9*n+1 \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Artur Jasinski, Oct 10 2007
STATUS
approved