This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A182592 Number of prime factors of form cn+1 for numbers 5^n-1 0
 1, 1, 1, 2, 2, 1, 1, 2, 3, 1, 2, 1, 3, 3, 2, 2, 3, 3, 3, 3, 4, 2, 3, 4, 3, 4, 3, 3, 5, 2, 3, 3, 4, 6, 3, 3, 6, 3, 5, 2, 6, 2, 3, 4, 4, 1, 2, 1, 6, 5, 3, 3, 7, 5, 3, 2, 5, 2, 7, 3, 5, 6, 4, 4, 7, 5, 8, 6, 8, 2, 3, 3, 6, 5, 5, 3, 7, 3, 4, 2, 6, 3, 3, 3, 6, 4, 4, 6, 5, 3, 2, 5, 4, 7, 5, 3, 4, 5, 7, 3, 10, 4, 5, 8, 6, 5, 2, 4, 7, 3, 6, 8, 5, 10, 2, 3, 6, 5, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,4 LINKS S. Mustonen, On prime factors of numbers m^n+-1 EXAMPLE For n=10, 5^n-1=9765624=2^3*3*11*71*521 has three prime factors of the form cn+1, namely 11=n+1, 71=7n+1, 521=52n+1. Thus a(10)=3. MATHEMATICA m = 5; n = 2; nmax = 120; While[n <= nmax, {l = FactorInteger[m^n - 1]; s = 0;      For[i = 1, i <= Length[l],       i++, {p = l[[i, 1]];        If[IntegerQ[(p - 1)/n] == True, s = s + l[[i, 2]]]; }];      a[n] = s; } n++; ]; Table[a[n], {n, 2, nmax}] Table[Count[FactorInteger[5^n-1][[All, 1]], _?(Mod[#, n]==1&)], {n, 2, 130}] (* Harvey P. Dale, Dec 11 2016 *) CROSSREFS Sequence in context: A122915 A327193 A279522 * A030298 A098281 A207324 Adjacent sequences:  A182589 A182590 A182591 * A182593 A182594 A182595 KEYWORD nonn AUTHOR Seppo Mustonen, Nov 22 2010 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 December 8 01:46 EST 2019. Contains 329850 sequences. (Running on oeis4.)