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A230955
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Boustrophedon transform of nonprimes.
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7
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1, 5, 15, 40, 114, 371, 1422, 6334, 32238, 184655, 1175454, 8231308, 62882262, 520416569, 4638303786, 44292536061, 451160065069, 4882696090609, 55951575728713, 676777708544967, 8617001415386120, 115200823068725262, 1613460678695102980, 23624702309844184487
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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LINKS
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J. Millar, N. J. A. Sloane and N. E. Young, A new operation on sequences: the Boustrophedon transform, J. Combin. Theory, 17A 44-54 1996 (Abstract, pdf, ps).
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FORMULA
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MATHEMATICA
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cc = Select[Range[max = 40], !PrimeQ[#]&]; t[n_, 0] := cc[[n+1]]; t[n_, k_] := t[n, k] = t[n, k-1] + t[n-1, n-k]; a[n_] := t[n, n]; Array[a, cc // Length, 0] (* Jean-François Alcover, Feb 12 2016 *)
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PROG
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(Haskell)
a230955 n = sum $ zipWith (*) (a109449_row n) a018252_list
(Python)
from itertools import accumulate, count, islice
from sympy import composite
def A230955_gen(): # generator of terms
yield 1
blist = (1, )
for i in count(1):
yield (blist := tuple(accumulate(reversed(blist), initial=composite(i))))[-1]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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