A066072 Prime numbers arising in A066071.
2, 3, 3, 5, 7, 5, 5, 7, 7, 13, 11, 13, 19, 13, 17, 17, 13, 19, 17, 13, 23, 17, 43, 19, 41, 37, 29, 17, 31, 37, 37, 41, 37, 61, 41, 43, 41, 73, 61, 47, 73, 43, 61, 41, 53, 37, 41, 73, 37, 89, 73, 59, 97, 61, 61, 101, 37, 41, 109, 67, 73, 71, 113, 73, 73, 41, 73, 97, 61, 79, 83
Offset: 1
Keywords
Examples
Solutions to 1+phi(x)=13 are {13, 21, 26, 28, 36, 42}; so 13 occur 5 times in the sequence in positions 10, 13, 15, 18 and 21, obtained as 1+Phi[m] values for 5 composite arguments.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)
Crossrefs
Programs
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Mathematica
Select[EulerPhi@ # + 1 & /@ Complement[Range@ #, Prime@ Range@ PrimePi@ #] &@ 168, PrimeQ] (* Michael De Vlieger, Jul 01 2016 *)
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PARI
{ n=0; for (m=1, 10^9, if (!isprime(m) && isprime(p=(eulerphi(m) + 1)), write("b066072.txt", n++, " ", p); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 10 2009
Formula
a(n) = 1 + phi(A066071(n)).