OFFSET
1,1
COMMENTS
If 2*p is in this sequence for a prime p, then p + 2 is the arithmetic mean of sigma(p + 1) and phi(p + 3). For the first four terms, primes p such that 2*p is in this sequence are 4679, 104831, 1450439, 99775079.
a(5) > 3*10^10. - Giovanni Resta, Sep 15 2017
EXAMPLE
PROG
(PARI) a001065(n) = sigma(n)-n;
a051953(n) = n-eulerphi(n);
isok(n) = a001065(a051953(n))-a051953(a001065(n))==n;
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Sep 13 2017
STATUS
approved