login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A235109 Averages q of twin prime pairs, such that q concatenated to q is also the average of a twin prime pair. 1
42, 102, 108, 180, 192, 270, 312, 420, 522, 660, 822, 882, 1230, 1482, 4242, 4788, 8820, 10332, 11550, 13692, 14550, 14562, 14868, 15732, 17910, 18522, 20550, 21648, 22620, 23670, 23832, 26262, 27738, 35838, 38922, 39042, 40128, 42018, 43962, 44532, 46440 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Michael G. Kaarhus, Table of n, a(n) for n = 1..770

EXAMPLE

192 is in this sequence, because 192 is an average of a twin prime pair, and so is 192192.

PROG

(Maxima) q:0$ for n:1 thru 800 step 0 do (q:q+6, if(primep(q-1) and primep(q+1)) then (b:concat(q, q), c:eval_string(b), if(primep(c-1) and primep(c+1)) then (if c>341550071728321 then (print("# ", c, " not determ."), n:5000), print(n, ", ", q), n:n+1 ) ) )$

(PARI) cat(n)=eval(concat(Str(n), n))

istwin(n)=n%6==5&&isprime(n)&&isprime(n+2)

v=List(); p=2; forprime(q=3, 1e10, if(q-p==2 && istwin(cat(p+1)-1), listput(v, p+1); if(#v==10^4, return)); p=q) \\ Charles R Greathouse IV, Jan 03 2014

CROSSREFS

Subsequence of A014574.

Sequence in context: A169738 A063329 A172465 * A039470 A241049 A075296

Adjacent sequences:  A235106 A235107 A235108 * A235110 A235111 A235112

KEYWORD

base,nonn

AUTHOR

Michael G. Kaarhus, Jan 03 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 September 18 12:35 EDT 2021. Contains 347527 sequences. (Running on oeis4.)