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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A255746 Squarefree semiprimes n such that n+4 is also a squarefree semiprime. 2
6, 10, 22, 34, 35, 51, 58, 65, 82, 87, 91, 111, 115, 118, 119, 129, 141, 142, 155, 183, 201, 202, 205, 209, 213, 214, 215, 217, 249, 274, 287, 291, 295, 298, 299, 301, 305, 319, 323, 335, 358, 377, 382, 391, 394, 403, 407, 411, 413, 447, 454, 469, 478, 481 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecturally, the sequence is infinite.

LINKS

Peter J. C. Moses, Table of n, a(n) for n = 1..1000

FORMULA

A000005(a(n)) = A000005(a(n)+4) = 4.

EXAMPLE

65 = 5*13; 65 + 4 = 69 = 3*23. So 65 is in the sequence.

MATHEMATICA

Select[Range@ 500, And[SquareFreeQ@ #, PrimeOmega@ # == 2, SquareFreeQ[# + 4], PrimeOmega[# + 4] == 2] &] (* Michael De Vlieger, Jul 12 2015 *)

PROG

(PARI) main(size)={ v=vector(size); i=0; m=1; while(i<size, if(omega(m)==2&&omega(m+4)==2&&issquarefree(m)&&issquarefree(m+4), v[i++]=m); m++; ); return(v); } /* Anders Hellström, Jul 11 2015 */

CROSSREFS

Cf. A000005, A001358, A005117, A175648.

Sequence in context: A102783 A157037 A189992 * A082917 A001172 A108605

Adjacent sequences:  A255743 A255744 A255745 * A255747 A255748 A255749

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Jul 11 2015

EXTENSIONS

More terms from Peter J. C. Moses, Jul 11 2015

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 18 21:04 EST 2018. Contains 317331 sequences. (Running on oeis4.)