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

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A281493 Numbers k such that (10^k + 41)/3 is prime. 0
 1, 2, 3, 4, 5, 8, 11, 13, 19, 46, 70, 98, 152, 187, 364, 425, 601, 665, 1837, 2267, 7691, 10246, 19988, 54290, 58571, 181996 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that k-2 occurrences of the digit 3 followed by the digits 47 is prime (see Example section). a(27) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 3w47. EXAMPLE 3 is in this sequence because (10^3 + 41)/3 = 347 is prime. Initial terms and primes associated: a(1) = 1, 17; a(2) = 2, 47; a(3) = 3, 347; a(4) = 4, 3347; a(5) = 5, 33347; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(10^# + 41)/3] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A322531 A302591 A269571 * A181341 A174181 A298424 Adjacent sequences:  A281490 A281491 A281492 * A281494 A281495 A281496 KEYWORD nonn,more,hard AUTHOR Robert Price, Jan 22 2017 EXTENSIONS a(26) from Robert Price, Dec 27 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 23 21:51 EST 2020. Contains 338603 sequences. (Running on oeis4.)