A340214 - OEIS

A340214

a(n) is the least m such that A340212(m) = 2*n.

3, 55, 4, 30, 37, 11, 25, 363, 31, 13, 312, 10, 78, 16, 67, 53, 243, 26, 35, 74, 39, 235, 709, 102, 224, 1192, 33, 207, 103, 94, 192, 940, 19, 833, 633, 99, 64, 680, 261, 434, 3994, 105, 743, 988, 68, 367, 168, 440, 177, 1874, 36, 567, 3810, 468, 250, 1006, 52, 226, 1514, 38, 1313, 3277, 160, 737

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OFFSET

1,1

COMMENTS

2*n*prime(a(n))+prime(a(n)-1) and 2*n*prime(a(n))+prime(a(n)+1) are prime.

LINKS

Robert Israel, Table of n, a(n) for n = 1..910

EXAMPLE

For n=4, A340212(30)=8 and this is the first appearance of 8 in A340212, so a(4)=30.

MAPLE

V:= Vector(60): count:= 0:

q:= 3: r:= 5:

for i from 3 while count < 60 do

p:= q; q:= r; r:= nextprime(r);

for k from 2 by 2 do

if isprime(k*q+p) and isprime(k*q+r) then break fi;

od;

v:= k/2;

if v <= 60 and V[v] = 0 then count:= count+1; V[v]:= i; fi

od:

PROG

(PARI) f(n) = my(p=prime(n), k=1); while (! (isprime(k*p+precprime(p-1)) && isprime(k*p+nextprime(p+1))), k++); k; \\ A340212

a(n) = my(m=3); while (f(m) != 2*n, m++); m; \\ Michel Marcus, Jan 01 2021

CROSSREFS

Cf. A340211, A340212.

Sequence in context: A334248 A193256 A319038 * A088278 A242199 A268661

Adjacent sequences: A340211 A340212 A340213 * A340215 A340216 A340217

KEYWORD

nonn

AUTHOR

J. M. Bergot and Robert Israel, Dec 31 2020

STATUS

approved