A066072 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = 1 + phi(A066071(n)).

EXAMPLE

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.

MATHEMATICA

Select[EulerPhi@ # + 1 & /@ Complement[Range@ #, Prime@ Range@ PrimePi@ #] &@ 168, PrimeQ] (* Michael De Vlieger, Jul 01 2016 *)

PROG

(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

CROSSREFS

Cf. A000010, A058340, A066071, A066072, A066073, A066074, A066075, A066076, A066077, A066080.

Sequence in context: A077558 A122444 A373751 * A239586 A180611 A084127

Adjacent sequences: A066069 A066070 A066071 * A066073 A066074 A066075

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 03 2001

STATUS

approved