

A124136


a(n) is the smallest prime when larger number of primes arise between numbers and their doubles. Note for example that there are 8 primes between 34 and 2*34=68 and 35 and 2*35=70, but 34 and 35 are not primes and a(8)=37, which is the smallest prime where there are already nine primes between numbers 36, 37, 38, 39, 41, 43, 44, 47, 48 and their doubles.


1



2, 7, 11, 17, 23, 29, 31, 37, 53, 59, 71, 79, 89, 97, 101, 127, 137, 149, 157, 179, 191, 211, 223, 233, 251, 257, 263, 293, 307, 311, 331, 347, 367, 373, 379, 389, 409, 419, 431, 443, 457, 479, 487, 499, 521, 541, 547, 557, 563, 587, 599, 613, 617, 631, 641
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OFFSET

1,1


COMMENTS

a(n) is the index of first occurrence of prime n in A060715.


LINKS

Table of n, a(n) for n=1..55.


EXAMPLE

a(2)=7 since 7 is first prime when two primes are between 7 and its double.
a(10)=59 since 59 is first prime after 55 and 56 when ten primes are between these numbers and their doubles.


MAPLE

ts_c:=proc(n) local i, j, st_p, max_stp, ans; ans:= [ ]: st_p:=0: max_stp:=0: for i from 2 to n do for j from i+1 to 2*i1 do if (isprime(j) = 'true') then st_p:=st_p+1: fi od: if (st_p > max_stp and isprime(i) = 'true') then max_stp := st_p: ans:=[ op(ans), i ]: fi; st_p:=0: od: RETURN(ans) end: ts_c(1200);


CROSSREFS

Cf. A060756, A060715, A084139.
Sequence in context: A168421 A038942 A175283 * A156828 A019385 A075552
Adjacent sequences: A124133 A124134 A124135 * A124137 A124138 A124139


KEYWORD

nonn,uned


AUTHOR

Jani Melik, Nov 30 2006


STATUS

approved



