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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A090261 Beginning with a(1) = 1, choose a(n+1) so that concatenation a(n+1), a(n), a(n+1) is a new prime. 2
1, 3, 1, 9, 1, 17, 1, 21, 11, 13, 17, 7, 3, 11, 19, 9, 7, 111, 17, 13, 23, 1, 27, 17, 37, 3, 13, 33, 23, 7, 129, 11, 27, 43, 3, 17, 39, 17, 103, 3, 19, 17, 121, 117, 1, 29, 1, 39, 23, 9, 13, 51, 1, 41, 3, 37, 21, 13, 53, 1, 47, 1, 51, 7, 131, 7, 137, 19, 23, 13, 71, 7, 149, 1, 59, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

H. v. Eitzen, Table of n, a(n) for n = 1..10000.

EXAMPLE

313, 131, 919, 191, 17117, 1171, 21121, etc. are primes.

PROG

(PARI) tp(n)=10^ceil(log(n+0.5)/log(10)); seen=Set([]); a=[1]; while(#a<100, n=a[ #a]; tn=tp(n); k=1; while(!isprime(z=(k*tn+n)*tp(k)+k) || setsearch(seen, z), k+=2); seen=setunion(seen, [z]); a=concat(a, k)); a \\ Hagen von Eitzen, Jun 21 2009

CROSSREFS

Cf. A090260.

Sequence in context: A197259 A200006 A070894 * A303552 A130599 A157674

Adjacent sequences:  A090258 A090259 A090260 * A090262 A090263 A090264

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Nov 28 2003

EXTENSIONS

a(14) corrected and more terms added by Hagen von Eitzen, Jun 21 2009

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 November 29 11:56 EST 2020. Contains 338766 sequences. (Running on oeis4.)