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A087747 Least number expressible as a sum of two distinct primes in exactly n ways. 2
5, 16, 24, 36, 48, 60, 78, 84, 90, 114, 144, 120, 168, 180, 234, 246, 288, 240, 210, 324, 300, 360, 474, 330, 528, 576, 390, 462, 480, 420, 570, 510, 672, 792, 756, 876, 714, 798, 690, 1038, 630, 1008, 930, 780, 960, 870, 924, 900, 1134, 1434, 840, 990, 1302, 1080, 1230, 1518 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..1000

EXAMPLE

a(2)=16 because we have 16=3+13=5+11, followed by 18=5+13=7+11; 20=3+17=7+13; 22=3+19=5+17; 26=3+23=7+19;...

MAPLE

P:=proc(h) local a, k, n, t, w; w:=array(1..h);

for n from 1 to h do w[n]:=0; od; t:=0;

for n from 1 to 10^10 do a:=0; for k from 2 to trunc(n/2) do

if isprime(k) and isprime(n-k) and n<>2*k then a:=a+1; fi; od;

if a>0 and a<=h then if w[a]=0 then w[a]:=n; t:=t+1; if t=h then break;

fi; fi; fi; od; print(w); end: P(1000); # Paolo P. Lava, May 26 2014

MATHEMATICA

Module[{nn=2000, ip}, ip=Table[{n, Length[Select[IntegerPartitions[n, {2}], #[[1]]!=#[[2]]&&AllTrue[#, PrimeQ]&]]}, {n, nn}]; Table[SelectFirst[ip, #[[2]]==k&], {k, 60}]][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 11 2020 *)

CROSSREFS

Sequence in context: A278415 A063243 A063232 * A352754 A090785 A069482

Adjacent sequences: A087744 A087745 A087746 * A087748 A087749 A087750

KEYWORD

nonn

AUTHOR

Lekraj Beedassy, Oct 02 2003

EXTENSIONS

More terms from John Dethridge (jcd(AT)ms.unimelb.edu.au), Jan 08 2004

More terms from Hugo Pfoertner, Sep 23 2004

Reinserted a(18), a(19) and a(20) by Paolo P. Lava, May 26 2014

STATUS

approved

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Last modified December 3 16:52 EST 2022. Contains 358534 sequences. (Running on oeis4.)