A245177 Inefficient primes.
5, 13, 19, 23, 29, 31, 43, 53, 59, 61, 67, 73, 79, 83, 89, 97, 103, 131, 137, 151, 157, 163, 173, 179, 181, 191, 197, 199, 211, 229, 233, 239, 241, 281, 293, 307, 317, 347, 359, 367, 373, 379, 389, 397, 409, 419, 421, 431, 433, 443, 449
Offset: 1
Keywords
Links
- Robert Israel, Table of n, a(n) for n = 1..1428
- Tewodros Amdeberhan and Victor H. Moll, Involutions and their progenies, preprint, 2014.
- Tewodros Amdeberhan and Victor H. Moll, Involutions and their progenies, arXiv:1406.2356 [math.CO], 2014.
- Tewodros Amdeberhan and Victor H. Moll, Involutions and their progenies, Journal of Combinatorics, 6(4) (2015), 483-508.
Programs
-
Maple
N:= 1000: # to get all terms <= N I1:= proc(n) option remember; I1(n-1)+(n-1)*I1(n-2) end proc: I1(0):= 1: I1(1):= 1: Primes:= select(isprime,{2,seq(2*i+1,i=1..floor((N-1)/2))}): PP:= convert(Primes,`*`): A:= {}: for n from 1 to N-1 do g:= igcd(I1(n),PP): A:= A union select(`>`,numtheory:-factorset(g),n); od: A; # Robert Israel, Jul 20 2014 -
Mathematica
A85 = DifferenceRoot[Function[{y, n}, {(-n-1) y[n] - y[n+1] + y[n+2] == 0, y[1] == 1, y[2] == 2}]]; inefficientQ[p_] := AnyTrue[Range[p-1], Divisible[A85[#], p]&]; Reap[For[p = 2, p < 1000, p = NextPrime[p], If[inefficientQ[p], Print[p]; Sow[p]]]][[2, 1]] (* Jean-François Alcover, Jul 28 2020 *)
Comments