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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A309740 Numbers k such that 5*10^(2*k) + 5*10^k + 1 are prime. 1
 0, 3, 5, 301 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 11 | 5*10^(4*m) + 5*10^(2*m) + 1. So a(n) is odd for n > 1. LINKS EXAMPLE 11 is prime ==> a(1) = 0.           551 = 19 * 29.         50501 = 11 * 4591.       5005001 is prime ==> a(2) = 3.     500050001 = 11 * 61 * 745231.   50000500001 is prime ==> a(3) = 5. 5000005000001 = 11 * 31 * 1801 * 8141461. PROG (PARI) for(k=0, 1e3, if(ispseudoprime(5*100^k+5*10^k+1), print1(k", "))) CROSSREFS Cf. A309739. Sequence in context: A101331 A232239 A087368 * A280035 A087670 A271390 Adjacent sequences:  A309737 A309738 A309739 * A309741 A309742 A309743 KEYWORD nonn,base,more AUTHOR Seiichi Manyama, Aug 15 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 April 22 21:05 EDT 2021. Contains 343177 sequences. (Running on oeis4.)