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



Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A231207 The primes given as concatenation of chunks of A231206 whose lengths (in number of terms) are given by the terms of A231206. 2
23, 149, 5, 67819, 1011121314151617139, 1820212259, 232425262763, 28293031323371, 3435363738394057, 414243444546474849505152535455565860109, 616264656667686970189, 72737475767778798081179, 8283848586878889909192173 (list; graph; refs; listen; history; text; internal format)



The n-th term is the concatenation of (the "next") A231206(n) terms of A231206.

The last term of A231206 used to produce the n-th prime is usually roughly twice as large as its neighbors, see example. This in turn leads to primes about twice as long as their neighbors in this sequence.


M. F. Hasler, Table of n, a(n) for n = 1..51


Concatenation of the first A231206(1)=2 terms of A231206 yields the first prime a(1)=23. Concatenation of the next A231206(2)=3 terms of A231206 yields a(2)=149.

The terms of A231206 in which ends the primes a(n) are usually roughly twice as large as their neighbors: ... 4, 9, 5,... 9, 19, 10,... 25, 59, 26,... 27, 63, 28,... 33, 71, 34,... 60, 109, 61,... 70, 198, 72,... 81, 179, 82,... But to make the 5th prime, the term A231206(19)=139 had to be chosen much larger than its neighbors (17 and 18), which in turn leads to the 417 digit prime a(19), concatenation of A231206(173..311). To get this prime, one has to take A231206(311)=581 roughly twice as large as his neighbors A231206(310)=309 and A231206(312)=310. This leads later again to a prime roughly twice as long as its neighbors in this sequence.


(PARI) {a=[prefix=2]; remain=pointer=1; for(n=1, 499, my(used=Set(a)); if( !remain, remain=a[pointer++]; print1(prefix", "); prefix=""); for(i=1, 1e9, setsearch(used, i) && next; remain>1 || ispseudoprime( eval( Str( prefix, i ))) || next; prefix=Str(prefix, i); a=concat(a, i); remain--; break ))}


Sequence in context: A055827 A255418 A268778 * A142902 A125333 A126491

Adjacent sequences: A231204 A231205 A231206 * A231208 A231209 A231210




M. F. Hasler, Nov 05 2013



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 December 9 18:21 EST 2022. Contains 358703 sequences. (Running on oeis4.)