OFFSET
1,1
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
A073490(a(n)) = 1.
EXAMPLE
200 is a term, as 200 = 2*2*2*5*5 with one gap between 2 and 5.
MATHEMATICA
pa[n_, k_] := If[k == NextPrime[n], 0, 1]; Select[Range[130], Total[pa @@@ Partition[First /@ FactorInteger[#], 2, 1]] == 1 &] (* Jayanta Basu, Jul 01 2013 *)
PROG
(Haskell)
a073493 n = a073493_list !! (n-1)
a073493_list = filter ((== 1) . a073490) [1..]
-- Reinhard Zumkeller, Dec 20 2013
(Python)
from sympy import primefactors, nextprime
def ok(n):
pf = primefactors(n)
return sum(p2 != nextprime(p1) for p1, p2 in zip(pf[:-1], pf[1:])) == 1
print(list(filter(ok, range(1, 130)))) # Michael S. Branicky, Oct 14 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Aug 03 2002
STATUS
approved