A234093 Integers of the form (p*q - 1)/2, where p and q are distinct primes.

7, 10, 16, 17, 19, 25, 27, 28, 32, 34, 38, 42, 43, 45, 46, 47, 55, 57, 59, 61, 64, 66, 70, 71, 72, 77, 79, 80, 88, 91, 92, 93, 100, 101, 102, 104, 106, 107, 108, 109, 110, 117, 118, 123, 124, 126, 129, 132, 133, 143, 145, 147, 149, 150, 151, 152, 154, 159

Offset

1,1

Comments

A102770 is subsequence. - Zak Seidov, Feb 21 2014

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Example

(3*5 - 1)/2 = 7; (3*7 - 1)/2 = 10.

Mathematica

t = Select[Range[1, 7000, 2], Map[Last, FactorInteger[#]] == Table[1, {2}] &]; Take[(t - 1)/2, 120] (* A234093 *)
v = Flatten[Position[PrimeQ[(t - 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}]  (* A233561 *)
(w - 1)/2 (* A234095 *) (* Peter J. C. Moses, Dec 23 2013 *)
With[{nn=60}, Take[Union[Select[(Times@@#-1)/2&/@Subsets[Prime[ Range[ nn]], {2}], IntegerQ]], nn]] (* Harvey P. Dale, Mar 08 2015 *)

Crossrefs

Cf. A102770, A233561, A234095, A234096.

Sequence in context: A020743 A088350 A083390 * A287567 A301451 A033817

Adjacent sequences: A234090 A234091 A234092 * A234094 A234095 A234096

Keyword

nonn,easy

Author

Clark Kimberling, Dec 27 2013

Status

approved