login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A128907 Semiprimes pq such that p, q are odd primes and p < q <= 4p+11. 2
15, 21, 33, 35, 39, 51, 55, 57, 65, 69, 77, 85, 91, 95, 115, 119, 133, 143, 145, 155, 161, 187, 203, 209, 217, 221, 247, 253, 259, 299, 319, 323, 341, 377, 391, 403, 407, 437, 451, 473, 481, 493, 517, 527, 533, 551, 559, 583, 589, 611, 629, 667 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These semiprimes, a subset of A046388, appear in Ng. Abstract: "Let H be a Hopf algebra of dimension pq over an algebraically closed field of characteristic zero, where p, q are odd primes with p < q < 4p+12. We prove that H is semisimple and thus isomorphic to a group algebra, or the dual of a group algebra."

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Siu-Hung Ng, Hopf algebras of dimension pq, II

FORMULA

{p*q such that p, q are odd primes and p < q <= 4*p+11}.

MATHEMATICA

pqopQ[n_]:=Module[{f=FactorInteger[n], f1}, f1=f[[All, 1]]; Length[f1]== 2 && Min[f1]>2&&Max[f[[All, 2]]]==1&&f1[[2]]<=4f1[[1]]+11]; Select[ Range[ 700], pqopQ] (* Harvey P. Dale, Sep 02 2016 *)

PROG

(PARI) is(n)=my(f=factor(n)); #f~==2 && f[1, 2]==1 && f[2, 2]==1 && f[1, 1]>2 && f[2, 1] <= 4*f[1, 1]+11 \\ Charles R Greathouse IV, Dec 30 2013

CROSSREFS

Cf. A000040, A001358, A046388.

Sequence in context: A046388 A056913 A002557 * A321644 A225709 A020162

Adjacent sequences:  A128904 A128905 A128906 * A128908 A128909 A128910

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Apr 21 2007

EXTENSIONS

Terms corrected by Charles R Greathouse IV, Dec 30 2013

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 17 19:51 EDT 2022. Contains 353778 sequences. (Running on oeis4.)