OFFSET
1,2
COMMENTS
Unit together with natural numbers n with number of nontrivial divisors equal to a perfect power. - Juri-Stepan Gerasimov, Oct 30 2009
This is wrong, e.g. a(29)=144, A000005(144)=15 and A075802(15-2)=0, see also example. - Reinhard Zumkeller, Jul 12 2013
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
PROG
(Haskell)
a081619 n = a081619_list !! (n-1)
a081619_list = filter ((== 1) . a010054 . a000005) [1..]
-- Reinhard Zumkeller, Jul 12 2013
(PARI) is(n)=ispolygonal(numdiv(n), 3) \\ Charles R Greathouse IV, Oct 16 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Mar 24 2003
EXTENSIONS
Example revised and extended by Reinhard Zumkeller, Jul 12 2013
STATUS
approved