OFFSET
1,2
COMMENTS
A019278 is the sequence of integers x such that sigma(sigma(x))/x is an integer.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..38
EXAMPLE
8 is a term since both 8 and 15=sigma(8) are terms of A019278.
PROG
(PARI) isok(n) = my(sn=sigma(n), ssn=sigma(sn)); (denominator(ssn/n)==1) && (denominator(sigma(ssn)/sn) == 1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Sep 27 2017
STATUS
approved