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A074719
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ip(n): the number of primes not exceeding reverse(n).
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2
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0, 1, 2, 2, 3, 3, 4, 4, 4, 0, 5, 8, 11, 13, 15, 18, 20, 22, 24, 1, 5, 8, 11, 13, 15, 18, 20, 22, 24, 2, 6, 9, 11, 14, 16, 18, 21, 23, 24, 2, 6, 9, 11, 14, 16, 18, 21, 23, 24, 3, 6, 9, 11, 14, 16, 18, 21, 23, 24, 3, 6, 9, 11, 14, 16, 18, 21, 23, 24, 4, 7, 9, 12, 15, 16, 19, 21, 23, 25
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| "ip" is "pi" backwards.
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FORMULA
| ip(n) = pi(reverse(n)).
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EXAMPLE
| ip(12) = pi(21) = 8.
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MATHEMATICA
| rev[n_] := FromDigits[Reverse[IntegerDigits[n]]]; f[n_] := Module[{r, i}, r = 0; i = 1; While[Prime[i] <= n, i++ ]; i - 1]; Table[f[rev[n]], {n, 1, 100}]
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CROSSREFS
| Cf. A000720.
Sequence in context: A059998 A036041 A085654 * A079730 A035486 A172397
Adjacent sequences: A074716 A074717 A074718 * A074720 A074721 A074722
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KEYWORD
| base,easy,nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Sep 27 2002
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