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A254285 Hexagonal numbers (A000384) which are also centered triangular numbers (A005448). 3
1, 1891, 26335, 71156485, 991081981, 2677903145191, 37298379237211, 100780206894952201, 1403687203222107385, 3792762303606727977835, 52826364168762410080471, 142736816433155393822880781, 1988067387723517337746328821, 5371757345852607787523567324911 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = a(n-1)+37634*a(n-2)-37634*a(n-3)-a(n-4)+a(n-5).
G.f.: -x*(x^4+1890*x^3-13190*x^2+1890*x+1) / ((x-1)*(x^2-194*x+1)*(x^2+194*x+1)).
EXAMPLE
1891 is in the sequence because it is the 31st hexagonal number and the 36th centered triangular number.
PROG
(PARI) Vec(-x*(x^4+1890*x^3-13190*x^2+1890*x+1)/((x-1)*(x^2-194*x+1)*(x^2+194*x+1)) + O(x^100))
CROSSREFS
Sequence in context: A151773 A020321 A177086 * A035869 A045198 A020417
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jan 28 2015
STATUS
approved

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Last modified May 26 12:53 EDT 2024. Contains 372826 sequences. (Running on oeis4.)