A131825 Numbers k such that cototient(x) = k has exactly 1 solution.
0, 2, 3, 5, 6, 14, 18, 20, 22, 28, 38, 40, 42, 62, 66, 68, 74, 76, 78, 82, 98, 102, 104, 106, 114, 124, 126, 136, 148, 156, 178, 194, 196, 200, 204, 208, 226, 242, 246, 248, 254, 258, 262, 296, 302, 306, 308, 314, 330, 338, 342, 356, 370, 374, 378, 388, 398, 400, 408, 416, 418, 422, 426, 434, 438
Offset: 1
Keywords
Examples
6 = cototient(10) and for all x<>10, cototient(x) <> 6.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..15628 (terms below 10^5; terms 1..316 from Robert Israel)
Programs
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Maple
N:= 1000: # for all terms <= N cotot:= n -> n - numtheory:-phi(n): V:= Vector(N): for n from 2 to N^2 do v:= cotot(n); if v > N then next fi; V[v]:= V[v]+1; od: 0, op(select(t -> V[t]=1, [$1..N])); # Robert Israel, May 26 2019
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PARI
lista(nn) = {my(v=vector(nn^2+2, i, i - eulerphi(i))); for(k=0, nn, if(sum(i=1, k*k+2, k==v[i])==1, print1(k, ", "))); } \\ Jinyuan Wang, Mar 21 2020
Extensions
More terms from Robert Israel, May 26 2019