OFFSET
1,4
COMMENTS
Numbers n such that a(a(n + 1)) = 1: 1 U primes U pseudoprimes;
a(n) such that a(n - 1) = 1: 1 U 1 U odd primes U pseudoprimes.
EXAMPLE
a(1) = (2*(1*Denominator(((1-1)*(1^2)+2^(1+1)-4)/(2*1))-1)/1+1 = 1.
PROG
(Magma) [2*(n*Denominator(((n-1)*(n^2)+2^(n+1)-4)/(2*n))-n)/n+1: n in [1..100]];
(PARI) a(n) = 2*(n*denominator(((n-1)*(n^2)+2^(n+1)-4)/(2*n))-n)/n + 1; \\ Michel Marcus, Sep 03 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Sep 01 2014
STATUS
approved