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!)
A309851 Primes formed by concatenating n and 2n-1. 1
11, 23, 47, 59, 1019, 1223, 1427, 1733, 2039, 2141, 2243, 2447, 2549, 2753, 2957, 3467, 3671, 4079, 4283, 4691, 4793, 5099, 52103, 55109, 61121, 65129, 70139, 75149, 77153, 82163, 86171, 95189, 102203, 104207, 112223, 119237, 124247, 130259, 132263, 137273, 145289, 146291, 147293, 149297, 150299, 160319 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..10000

MATHEMATICA

f[n_] := FromDigits @ (Join @@ IntegerDigits[{n, 2n-1}]); Select[f /@ Range[160], PrimeQ]  (* Amiram Eldar, Sep 24 2019 *)

PROG

(MAGMA) [a:m in [1..170]|IsPrime(a) where a is 10^(#Intseq(2*m-1))*m+2*m-1]; // Marius A. Burtea, Oct 09 2019

(Python)

from sympy import isprime

A309851_list = [m for m in (int(str(n)+str(2*n-1)) for n in range(1, 10**5)) if isprime(m)] # Chai Wah Wu, Oct 23 2019

CROSSREFS

Cf. A000040, A052089 (n and n-1), A030458 (n and n+1), A309808 (n and 2n+1).

Sequence in context: A073024 A161897 A282531 * A145994 A217047 A139834

Adjacent sequences:  A309848 A309849 A309850 * A309852 A309853 A309854

KEYWORD

nonn,base

AUTHOR

A.H.M. Smeets, Aug 20 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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 19 16:01 EDT 2021. Contains 345144 sequences. (Running on oeis4.)