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A298244
a(n) = n! * [x^n] (sec(x) + tan(x))^n.
1
1, 1, 4, 30, 320, 4400, 74016, 1472240, 33800192, 879646464, 25589632000, 822867814912, 28982612385792, 1109640105852928, 45884917741981696, 2038015221365667840, 96765606087737999360, 4890992991269273403392, 262201755871367895711744, 14859866059895961631981568, 887693530413229611155456000
OFFSET
0,3
FORMULA
a(n) ~ n! * c * d^n / sqrt(n), where d = 3.063838405249746742835218125232... and c = 0.308377491585051819518915209... - Vaclav Kotesovec, Aug 17 2019
MATHEMATICA
Table[n! SeriesCoefficient[(Sec[x] + Tan[x])^n, {x, 0, n}], {n, 0, 20}]
CROSSREFS
Main diagonal of A322267.
Sequence in context: A243244 A293022 A360766 * A293191 A367963 A180623
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jan 15 2018
STATUS
approved