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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A099073 Numbers n such that the concatenation of the first n-1 odd primes in decreasing order is prime. 1
2, 3, 7, 24, 76, 1100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A100003(n)=prime(a(n)). Next term is greater than 4500 and the prime corresponding to the next term has more than 21000 digits. Number of digits of primes corresponding to the six known terms of the sequence are respectively 1,2,9,43,198 & 4202. There is no known prime formed by concatenation of the first n odd primes with increasing order for 1<n<2250.

LINKS

Table of n, a(n) for n=1..6.

C. Rivera, Primes by Listing.

EXAMPLE

7 is in the sequence because the first 6 odd primes are 3,5,7,11,13,17 and 17.13.11.7.5.3 is prime (dot between numbers means concatenation).

MATHEMATICA

Do[If[PrimeQ[(v={}; Do[v=Join[v, IntegerDigits[Prime[n-j+1]]], {j, n-1}]; FromDigits[v])], Print[n]], {n, 2, 4500}]

Select[Range[1100], PrimeQ[FromDigits[Flatten[IntegerDigits/@ Reverse[ Prime[ Range[ 2, #]]]]]]&] (* Harvey P. Dale, Nov 12 2017 *)

CROSSREFS

Cf. A046035, A099070, A099071.

Sequence in context: A296397 A102710 A048824 * A129724 A308161 A094697

Adjacent sequences:  A099070 A099071 A099072 * A099074 A099075 A099076

KEYWORD

base,more,nonn,nice

AUTHOR

Farideh Firoozbakht, Nov 06 2004

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 December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)