

A074719


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


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
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OFFSET

1,3


COMMENTS

"ip" is "pi" backwards.


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


FORMULA

ip(n) = pi(reverse(n)).


EXAMPLE

ip(12) = pi(21) = 8.


MAPLE

reverse:= proc(n) local L, d;
L:= convert(n, base, 10);
add(10^(i1)*L[i], i=1..nops(L));
end proc:
map(numtheory:pi @ reverse, [$1..100]); # Robert Israel, Jan 04 2017


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}]
PrimePi[FromDigits[Reverse[IntegerDigits[#]]]]&/@Range[80] (* Harvey P. Dale, May 28 2015 *)


CROSSREFS

Cf. A000720, A004086.
Sequence in context: A036041 A252759 A085654 * A079730 A035486 A282347
Adjacent sequences: A074716 A074717 A074718 * A074720 A074721 A074722


KEYWORD

base,easy,nonn,look


AUTHOR

Joseph L. Pe, Sep 27 2002


STATUS

approved



