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A281687
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Number of partitions of 2*n into the sum of two totient numbers (A002202).
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4
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1, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 7, 6, 7, 7, 9, 8, 9, 8, 9, 9, 11, 10, 12, 10, 11, 10, 12, 11, 13, 10, 11, 12, 13, 12, 15, 13, 12, 13, 13, 12, 15, 14, 14, 14, 16, 15, 19, 16, 16, 16, 17, 15, 19, 15, 18, 16, 19, 16, 20, 18, 19, 18, 20, 17, 22, 19, 21, 18, 21, 19, 22
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OFFSET
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1,4
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COMMENTS
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LINKS
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EXAMPLE
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a(6) = 3 because 2 * 6 = 12 = 2 + 10 = 4 + 8 = 6 + 6 and 2, 4, 6, 8, 10 are in A002202.
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MAPLE
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N:= 1000: V:= Vector(2*N):
V[1]:= 1:
for n from 2 to 2*N by 2 do
if nops(numtheory:-invphi(n))>1 then V[n]:= 1 fi
od:
C:= map(round, SignalProcessing:-Convolution(V, V)):
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PROG
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(PARI) a(n) = sum(k=1, n, istotient(k) && istotient(2*n-k));
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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