login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A241764 Semiprimes sp such that sp-3 is also semiprime. 2
9, 25, 38, 49, 58, 65, 77, 85, 94, 118, 121, 122, 145, 146, 158, 161, 169, 205, 206, 209, 217, 218, 221, 262, 265, 298, 301, 302, 305, 326, 329, 358, 361, 365, 394, 398, 454, 469, 481, 485, 505, 514, 517, 529, 538, 545, 554, 562, 565, 586, 589, 614 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also semiprimes of the form 2^x - x.

The primes of the form 2^x - x are in A081296.

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..1100

EXAMPLE

a(3)= 38 = 2*19, which is semiprime: 38-3 = 35 = 5*7 is also semiprime.

a(5)= 58 = 2*29, which is semiprime: 58-3 = 55 = 5*11 is also semiprime.

MAPLE

with(numtheory): A241764:= proc(); if bigomega(x)=2 and bigomega(x-3)=2 then RETURN (x); fi; end: seq(A241764 (), x=1..2000);

MATHEMATICA

Flatten[Position[Partition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 700}], 4, 1], _?(First[ #] ==Last[#]==1&), {1}, Heads->False]]+3 (* Harvey P. Dale, Dec 21 2015 *)

PROG

(PARI) for(k=1, 500, if(bigomega(k)==2 && bigomega(k-3)==2, print1(k, ", "))) \\ Colin Barker, May 07 2014

CROSSREFS

Cf. A001358, A092207, A123017, A198327.

Sequence in context: A226647 A147199 A147403 * A044451 A114057 A227518

Adjacent sequences:  A241761 A241762 A241763 * A241765 A241766 A241767

KEYWORD

nonn

AUTHOR

K. D. Bajpai, Apr 29 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 April 22 06:14 EDT 2019. Contains 322329 sequences. (Running on oeis4.)