login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A177880 Numbers such that not all exponents in prime power factorization are in A005836 1
4, 9, 12, 18, 20, 25, 28, 32, 36, 44, 45, 49, 50, 52, 60, 63, 64, 68, 72, 75, 76, 84, 90, 92, 96, 98, 99, 100, 108, 116, 117, 121, 124, 126, 128, 132, 140, 144, 147, 148, 150, 153, 156, 160, 164, 169, 171, 172, 175, 180, 188, 192, 196, 198, 200, 204, 207 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

1 and products of distinct numbers of the form P^(3^k), k>=0, are not in the sequence.

LINKS

Table of n, a(n) for n=1..57.

FORMULA

Let A(x) be counting function of terms not exceeding x. Then for x tends to infinity, A(x)=C*x+o(x^(0.5+eps), where C=1-Prod{i=p^(3^k)with prime p and k>=0}(1-1/(i^2+i+1)).

PROG

(Sage) is_A005836 = lambda n: 2 not in n.digits(base=3)

is_A177880 = lambda n: not all(is_A005836(Integer(m)) for p, m in factor(n)) # [D. S. McNeil, Dec 16 2010]

CROSSREFS

Cf. A005836

Sequence in context: A276885 A089910 A312862 * A059269 A081619 A304365

Adjacent sequences:  A177877 A177878 A177879 * A177881 A177882 A177883

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Dec 15 2010

EXTENSIONS

Extended by D. S. McNeil, Dec 16 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 05:56 EDT 2018. Contains 316202 sequences. (Running on oeis4.)