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 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 (list; graph; refs; listen; history; text; internal format)
 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^(i-1)*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

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Last modified September 28 13:24 EDT 2020. Contains 337393 sequences. (Running on oeis4.)