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A336408 a(n) = number of composites c+d such that c is a composite and d is the n-th odd composite. 3
1, 4, 7, 8, 10, 13, 15, 17, 20, 22, 24, 24, 26, 31, 33, 35, 38, 40, 43, 44, 46, 47, 49, 52, 53, 58, 63, 63, 64, 66, 66, 68, 71, 73, 75, 77, 79, 80, 82, 84, 89, 91, 91, 94, 98, 99, 102, 103, 105, 109, 110, 111, 114, 117, 120, 122, 123, 125, 128, 129, 131, 131 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
The n-th odd composite is A014076(n+1); the n-th composite is A002808(n).
LINKS
EXAMPLE
a(1) counts this sum: 6+9.
a(2) counts these sums: 6+15, 9+15, 10+15, 12+15.
a(3) counts these: 4+21, 6+21, 9+21, 12+21, 14+21, 15+21, 18+21.
MATHEMATICA
z = 400; p = Prime[Range[z]];
c = Select[Range[2, z], ! PrimeQ@# &]; (* A002808 *)
d = Select[Range[2, z], ! PrimeQ@# && OddQ@# &]; (* A014076 *)
f[n_] := Select[c, # < d[[n]] &];
g[n_] := d[[n]] + Select[c, # < d[[n]] &];
q[n_] := Length[Intersection[p, g[n]]];
tq = Table[q[n], {n, 1, 120}] (* A336406 *)
tc = Table[Length[f[n]], {n, 1, 120}] (* A336407 *)
m = Min[Length[tq], Length[tc]]; Take[tc, m] - Take[tq, m] (* A336408 *)
CROSSREFS
Sequence in context: A175553 A284684 A175008 * A286401 A084791 A310933
KEYWORD
nonn
AUTHOR
Clark Kimberling, Jul 20 2020
STATUS
approved

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Last modified June 17 20:03 EDT 2024. Contains 373464 sequences. (Running on oeis4.)