login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A234501 Products p*q*r*s of distinct primes for which (p*q*r*s + 1)/2 is prime. 3
1365, 3045, 4305, 4485, 4785, 4845, 5005, 5313, 6045, 6405, 7161, 7665, 8265, 8745, 9165, 9345, 9933, 10005, 10101, 10465, 10545, 10605, 10965, 11305, 11685, 12441, 12597, 13585, 14385, 14421, 14973, 15045, 15405, 15645, 15873, 16185, 16485, 17085, 17385 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..39.

EXAMPLE

1365 = 3*5*7*13, and (1365+1)/2 = 683, a prime.

MATHEMATICA

t = Select[Range[1, 20000, 2], Map[Last, FactorInteger[#]] == Table[1, {4}] &]; Take[(t + 1)/2, 120] (* A234500*)

v = Flatten[Position[PrimeQ[(t + 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}]  (* A234501 *)

(w + 1)/2 (* A234502 *)   (* Peter J. C. Moses, Dec 23 2013 *)

CROSSREFS

Cf. A234500, A234502, A234498, A234103.

Sequence in context: A043686 A043578 A004970 * A128285 A069310 A096117

Adjacent sequences:  A234498 A234499 A234500 * A234502 A234503 A234504

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Jan 01 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 4 11:09 EDT 2020. Contains 334825 sequences. (Running on oeis4.)