id:A074719 - OEIS Search Results

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ip(n): the number of primes not exceeding reverse(n).

+0
3

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; listen)

	OFFSET	`1,3`
	COMMENT	`"ip" is "pi" backwards.`
	FORMULA	`ip(n) = pi(reverse(n)).`
	EXAMPLE	`ip(12) = pi(21) = 8.`
	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}]`
	CROSSREFS	`Cf. A000720.` `Sequence in context: A059998 A036041 A085654 this_sequence A079730 A035486 A143489` `Adjacent sequences: A074716 A074717 A074718 this_sequence A074720 A074721 A074722`
	KEYWORD	`base,easy,nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Sep 27 2002`

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Last modified December 5 08:23 EST 2009. Contains 170348 sequences.

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