This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A283503 Numbers k such that (23*10^k - 59)/9 is prime. 0
 3, 6, 10, 16, 22, 30, 33, 48, 61, 66, 147, 300, 372, 925, 1750, 2026, 2721, 3916, 5704, 6856, 12883, 57333, 92244 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 5 followed by the digits 49 is prime (see Example section). a(24) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 25w49. EXAMPLE 6 is in this sequence because (23*10^6 - 59)/9 =  is prime. Initial terms and primes associated: a(1) = 3, 2549; a(2) = 6, 2555549; a(3) = 10, 25555555549; a(4) = 16, 25555555555555549; a(5) = 22, 25555555555555555555549; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(23*10^# - 59)/9] &] PROG (PARI) isok(n) = isprime((23*10^n - 59)/9); \\ Indranil Ghosh, Mar 09 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A264041 A260708 A025215 * A049697 A111712 A194144 Adjacent sequences:  A283500 A283501 A283502 * A283504 A283505 A283506 KEYWORD nonn,more,hard AUTHOR Robert Price, Mar 09 2017 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.