This site is supported by donations to The OEIS Foundation.

 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!)
 A309808 Primes formed by concatenating n and 2n+1. 4
 13, 37, 613, 919, 1021, 1123, 1327, 1429, 1531, 2143, 2347, 2551, 2857, 3061, 3163, 3469, 3571, 3673, 3877, 4591, 4999, 50101, 56113, 59119, 63127, 70141, 71143, 74149, 78157, 79159, 81163, 88177, 91183, 93187, 95191, 101203, 105211, 106213, 108217, 110221, 113227, 114229 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes in A309809. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(3)=613 is the concatenation of 6 and 2*6+1=13 and is prime. MAPLE select(isprime, [seq(n*10^(1+ilog10(2*n+1))+2*n+1, n=1..200)]); PROG (MAGMA) [a:m in [1..130]|IsPrime(a) where a is 10^(#Intseq(2*m+1))*m+2*m+1]; // Marius A. Burtea, Aug 18 2019 CROSSREFS Cf. A030458, A309809. Sequence in context: A098265 A195540 A262475 * A201809 A129541 A302858 Adjacent sequences:  A309804 A309805 A309806 * A309809 A309810 A309811 KEYWORD nonn,base AUTHOR J. M. Bergot and Robert Israel, Aug 17 2019 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.

Last modified December 9 00:32 EST 2019. Contains 329871 sequences. (Running on oeis4.)