This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A122787 a(n) is the smallest prime p such that the multiplicative order of 10 modulo p is 3^n. 1
 3, 37, 333667, 757, 163, 411361786890737698932559, 313471, 2558791, 618846643, 2238862519, 396319276163359, 34720813 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS For n>0, a(n) is the smallest prime p>3 such that 3^n*p but not 3^(n-1)*p is a solution to 10^x==1 (mod x). A014950 gives solutions of this equation. It's obvious that if n is a term of A014950 then 3n is also a term of A014950. So according to the definition of a(n), for each m>n-1, 3^m*a(n) is in the sequence A014950. a(n) is the smallest prime divisor of \Phi_{3^n}(10)/3, where \Phi_k(x) is k-th cyclotomic polynomial. a(n) is congruent to 1 modulo 3^n and 1, 3, 9, 13, 27, 31, 37, or 39 modulo 40. - Max Alekseyev, Nov 18 2014 a(12)>10^17, a(13)=796884087799, a(14)=86093443, a(15)=70367039929, a(16)>8*10^18, a(17)=662489036191, a(18)>10^19, a(19)>10^19, a(20)=38180289190951, a(21)=28305715767319, a(22)>10^20, a(23)>10^20, a(24)=63829075244707. - Ray Chandler, Dec 25 2013 LINKS J. Brillhart et al., Factorizations of b^n +- 1, b = 2, 3, 5, 6, 7, 10, 11, 12 Up to High Powers, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 2002. EXAMPLE p=333667 is the smallest prime such that multiplicative order of 10 modulo p is 3^2, so a(2)=333667. PROG (PARI) a(n) = factor(polcyclo(3^n, 10)/3)[1, 1] \\ Max Alekseyev, Nov 18 2014 CROSSREFS Cf. A014950, A066364. Sequence in context: A088098 A284411 A176245 * A241895 A093939 A129122 Adjacent sequences:  A122784 A122785 A122786 * A122788 A122789 A122790 KEYWORD hard,more,nonn AUTHOR Farideh Firoozbakht, Oct 06 2006 EXTENSIONS Revised and extended by Max Alekseyev, Apr 25 2009 a(13), a(15), a(17), a(20), a(21), a(24) from Ray Chandler, Dec 25 2013 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 20 17:54 EDT 2019. Contains 322310 sequences. (Running on oeis4.)