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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A047979 Let (p1,p2), (p3,p4) be pairs of twin primes with p1*p2=p3+p4-1; sequence gives values of p4. 4
19, 73, 883, 2593, 180001, 206083, 388963, 2268451, 2836963, 3612673, 6329683, 6415363, 10342153, 18800713, 28486153, 32080051, 40878883, 89753203, 97050313, 127552393, 154844803, 183169801, 230953033 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

EXAMPLE

E.g. 5*7=17+19-1,11*13=71+73-1.

PROG

(PARI) list(lim)=my(v=List(), p=3, r); forprime(q=5, sqrtint(lim\1*2-2)+1, if(q-p==2 && isprime(r=p*q\2) && isprime(r+2), listput(v, r+2)); p=q); Vec(v) \\ Charles R Greathouse IV, Sep 29 2015

(PARI) is(n)=my(p=sqrtint(2*n-3)); p*(p+2)==2*n-3 && isprime(n) && isprime(n-2) && isprime(p) && isprime(p+2) \\ Charles R Greathouse IV, Sep 29 2015

CROSSREFS

Cf. A047976-A047978.

Sequence in context: A220447 A294460 A118593 * A290241 A159997 A073566

Adjacent sequences:  A047976 A047977 A047978 * A047980 A047981 A047982

KEYWORD

nonn

AUTHOR

Naohiro Nomoto

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 August 18 08:57 EDT 2019. Contains 326077 sequences. (Running on oeis4.)