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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A270249 Greater of a pair of twin primes (r,s=r+2) where s is of the form p^2 + pq + q^2 and p and q are also twin primes. 0
109, 433, 2056753, 3121201, 3577393, 26462701, 37340353, 43823053, 128786113, 202705201, 304093873, 888345793, 1005988033, 1399680001, 1537437133, 2282300173, 2310187501, 2444964913, 2929312513, 3564542701, 5831255233, 7950571201, 8512439473, 9346947373, 9648752833, 12627464653, 15624660673 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A243761.

How is the distribution of terms of this sequence? With this form p^2 + pq + q^2, do twin primes generate bigger twin primes infinitely many times?

LINKS

Table of n, a(n) for n=1..27.

EXAMPLE

109 is a term because 109 and 107 are twin primes and 109 = 5^2 + 5*7 + 7^2, 5 and 7 are also twin primes.

433 is a term because 433 and 431 are twin primes and 433 = 11^2 + 11*13 + 13^2, 11 and 13 are also twin primes.

PROG

(PARI) t(n, p=3) = {while( p+2 < (p=nextprime( p+1 )) || n-->0, ); p-2}

for(n=1, 1e3, if(ispseudoprime(P=(3*t(n)^2 + 6*t(n) + 4)) && ispseudoprime(P-2), print1(P, ", ")));

CROSSREFS

Cf. A001359, A243761.

Sequence in context: A142846 A166560 A139644 * A174339 A142640 A126856

Adjacent sequences:  A270246 A270247 A270248 * A270250 A270251 A270252

KEYWORD

nonn

AUTHOR

Altug Alkan, Mar 14 2016

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 October 17 22:37 EDT 2019. Contains 328134 sequences. (Running on oeis4.)