OFFSET
1,2
COMMENTS
19289, 7391381, 9041581, 9124081, 9589141 are prime numbers. See A280555 for other prime terms of this sequence.
FORMULA
EXAMPLE
19289 is a term because sigma(19289) = 19290 and sigma(19290) = 46368 is a Fibonacci number.
PROG
(PARI) isFibonacci(n)=my(k=n^2); issquare(k+=(k+1)<<2) || (n>0 && issquare(k-8));
is(n)=isFibonacci(sigma(sigma(n)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Jan 05 2017
EXTENSIONS
More terms from Giovanni Resta, Jan 08 2017
STATUS
approved