The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A178313 Absolute difference between prime factors of n-th semiprime mod n. 2
 0, 1, 0, 3, 0, 2, 4, 1, 0, 1, 8, 3, 2, 3, 10, 5, 0, 14, 6, 16, 6, 7, 8, 20, 10, 4, 12, 12, 12, 26, 6, 28, 12, 14, 16, 34, 18, 19, 10, 0, 18, 38, 40, 12, 20, 44, 22, 2, 24, 21, 26, 25, 50, 16, 26, 0, 56, 29, 58, 32, 6, 33, 1, 35, 22, 36, 34, 8, 68, 35, 38, 24, 34, 70, 4, 35, 42, 76, 6, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..20000 EXAMPLE a(2)=1 because semiprime(2) = 6 = 3*2 and (3-2) mod 2 = 1. MATHEMATICA semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; f[n_] := Subtract @@ Reverse@ Flatten[ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@ n]; t = Select[ Range@ 215, semiPrimeQ]; Table[ Mod[ f[ t[[n]]], n], {n, 80}] f[{a_, b_}]:=Module[{c=FactorInteger[b][[;; , 1]]}, If[Length[c]==1, 0, Mod[Differences[c][[1]], a]]]; Module[{nn=300, spr}, spr=Select[Range[nn], PrimeOmega[#]==2&]; f/@Thread[{Range[ Length[ spr]], spr}]] (* Harvey P. Dale, May 29 2024 *) CROSSREFS Cf. A001358, A178102, A109313. Sequence in context: A112974 A113069 A136163 * A190013 A171088 A058624 Adjacent sequences: A178310 A178311 A178312 * A178314 A178315 A178316 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Dec 20 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 14 10:24 EDT 2024. Contains 375159 sequences. (Running on oeis4.)