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A247073
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Triangle read by rows: T(n,k) is the number of k-th prime powers up to 2^n, for k = 1 to n.
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1
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1, 2, 1, 4, 1, 1, 6, 2, 1, 1, 11, 3, 2, 1, 1, 18, 4, 2, 1, 1, 1, 31, 5, 3, 2, 1, 1, 1, 54, 6, 3, 2, 2, 1, 1, 1, 97, 8, 4, 2, 2, 1, 1, 1, 1, 172, 11, 4, 3, 2, 2, 1, 1, 1, 1, 309, 14, 5, 3, 2, 2, 1, 1, 1, 1, 1, 564, 18, 6, 4, 3, 2, 2, 1, 1, 1, 1, 1, 1028, 24, 8, 4, 3, 2, 2, 2, 1, 1, 1, 1, 1
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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LINKS
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EXAMPLE
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Up to 16, there are 6 primes (2, 3, 5, 7, 11, 13), 2 squared primes (4,9), 1 cube (8), and 1 fourth power (16), so 4th row is 6, 2, 1, 1.
Triangle starts:
1;
2, 1;
4, 1, 1;
6, 2, 1, 1;
11, 3, 2, 1, 1;
18, 4, 2, 1, 1, 1;
...
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PROG
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(PARI) tabl(nn) = {for (n=1, nn, v = vector(2^n, i, i); vr = vector(n); for (k=1, #v, if (pp = isprimepower(v[k]), vr[pp] ++); ); for (k=1, n, print1(vr[k], ", "); ); print(); ); }
(Haskell)
import Data.List (sort, groupBy); import Data.Function (on)
a247073 n k = a247073_tabl !! (n-1) !! (k-1)
a247073_tabl = map a247073_row [1..]
a247073_row n = map length $ groupBy ((==) `on` fst) $ sort $
takeWhile ((<= 2^n). snd) $ tail $ zip a025474_list a000961_list
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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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