A103767 Numbers n such that prime(n)*prime(n+1)*prime(n+2) - 1 is semiprime.

6, 10, 29, 42, 44, 55, 57, 102, 104, 111, 120, 136, 174, 184, 257, 269, 308, 325, 327, 401, 426, 504, 514, 565, 571, 594, 595, 652, 717, 755, 864, 882, 901, 907, 985, 1014, 1074, 1134, 1141, 1156, 1198, 1301, 1327, 1346, 1362, 1654, 1670, 1674, 1778, 1897

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

prime(10)*prime(11)*prime(12) - 1 = 29*31*37 - 1 = 33262= 2*16631, hence 10 is
a term.

Mathematica

PrimePi/@Transpose[Select[Partition[Prime[Range[2000]], 3, 1], PrimeOmega[ Times@@#-1]==2&]][[1]] (* Harvey P. Dale, Mar 15 2015 *)

Prog

(PARI) for(n=1, 1900, if(bigomega(prime(n)*prime(n+1)*prime(n+2)-1)==2, print1(n, ", ")))

Crossrefs

Cf. A001358, A006881, A103614, A103746.

Sequence in context: A300098 A240972 A349846 * A025129 A093559 A269697

Adjacent sequences: A103764 A103765 A103766 * A103768 A103769 A103770

Keyword

nonn,easy

Author

Klaus Brockhaus, Mar 29 2005

Status

approved