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A207575 Numbers n such that phi(n) + 2 divides n + 2 and n is not twice a prime. 1
1, 390, 10374 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(4) > 10^7.

a(4) > 3 * 10^10 if it exists. - Charles R Greathouse IV, Mar 02 2012

a(4) > 10^13, if it exists. - Giovanni Resta, May 05 2017

LINKS

Table of n, a(n) for n=1..3.

MATHEMATICA

Select[Range[20000000], !PrimeQ[#/2] && Divisible[#+2, EulerPhi[#]+2]&]

PROG

(PARI) for(n=1, 1e5, if((n+2)%(eulerphi(n)+2)==0&&(n%2||!isprime(n/2)), print1(n", "))) \\ Charles R Greathouse IV, Mar 02 2012

CROSSREFS

Cf.  A000010 (Euler's totient function).

Cf.  A207574 (Numbers n such that phi(n)+2 divides n+2).

Cf.  A202855 (Numbers n such that phi(n)-1 divides n).

Cf.  A203966 (Numbers n such that phi(n) divides n+1).

Sequence in context: A202429 A236612 A332419 * A318174 A158004 A264448

Adjacent sequences:  A207572 A207573 A207574 * A207576 A207577 A207578

KEYWORD

nonn,bref

AUTHOR

José María Grau Ribas, Feb 19 2012

STATUS

approved

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Last modified December 5 00:21 EST 2021. Contains 349530 sequences. (Running on oeis4.)