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A263674 Double interprimes: a(n) = (q+r)/2 = (p+s)/2 with p<q<r<s consecutive primes. 2
9, 12, 15, 18, 30, 42, 60, 81, 102, 105, 108, 120, 144, 165, 186, 195, 228, 260, 270, 312, 363, 381, 399, 420, 426, 441, 462, 489, 495, 552, 570, 582, 600, 696, 705, 714, 765, 816, 825, 858, 870, 882, 897, 924, 987, 1026, 1050, 1056, 1092, 1113, 1167, 1230 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Values of p (lesser of consecutive primes) are in the sequence A022885.

LINKS

Table of n, a(n) for n=1..52.

Eric Weisstein's World of Mathematics, Interprime

EXAMPLE

600 is in this sequence because 593, 599, 601 and 607 are consecutive primes, and 600 = (599+601)/2 = (593+607)/2.

MATHEMATICA

(Prime@ # + Prime[# + 3])/2 & /@ Select[Range@ 240, (First@ # + Last@ #)/2 == (#[[2]] + #[[3]])/2 &@ Prime@ Range[#, # + 3] & (* Michael De Vlieger, Nov 18 2015 *)

PROG

(PARI) {forprime(q=3, 2000, p=precprime(q-1); r=nextprime(q+1); s=nextprime(r+1); m=(q+r)/2; if(m==(p+s)/2, print1(m, ", ")))}

CROSSREFS

Cf. A022885, A075190, A075277, A075296, A078443, A130178, A263675, A263676.

Sequence in context: A161345 A102655 A120167 * A297667 A048699 A019468

Adjacent sequences:  A263671 A263672 A263673 * A263675 A263676 A263677

KEYWORD

nonn

AUTHOR

Antonio Roldán, Oct 23 2015

STATUS

approved

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Last modified January 23 00:58 EST 2018. Contains 298093 sequences.