A079164 Twin-primorial numbers: running products of twin primes.
3, 15, 75, 525, 5775, 75075, 1276275, 24249225, 703227525, 21800053275, 893802184275, 38433493923825, 2267576141505675, 138322144631846175, 9820872268861078425, 716923675626858725025, 72409291238312731227525
Offset: 1
Keywords
Examples
The first two twin primes are 3 and 5, so the first term is 3 and the second term is 15. The next two twin primes are 5 and 7, so the third term is 5*15=75 and the fourth term is 75*7=525
Links
- Amiram Eldar, Table of n, a(n) for n = 1..309
Crossrefs
Partial products of A077800.
Programs
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Mathematica
Rest[FoldList[Times,1,Flatten[Select[Partition[Prime[Range[30]], 2,1], Last[#]-First[#]==2&]]]] (* Harvey P. Dale, Mar 16 2011 *)
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PARI
twprfact(n) = {sr=0; tp = vector(10000); k=1; forprime(j = 3,n, if(nextprime(j+1)-j == 2, tp[k] = j; tp[k+1] = j+2; k+=2; ); ); for(j=1,k-1, y=1; for(i = 1,j, y*=tp[i]; ); print1(y", "); sr+=1.0/y; ); print(); print(sr); }
Extensions
Definition clarified and example provided by Harvey P. Dale, Mar 16 2011
Comments