login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A081311 Numbers that can be written as sum of a prime and an 3-smooth number. 7
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A081308(a(n))>0; complement of A081310.

Up to 10^n this sequence has 8, 95, 916, 8871, 86974, 858055, 8494293, 84319349, 838308086, ... terms. The lower density is of this sequence is greater than 0.59368 (see Pintz), but seems to be less than 1; can this be proved? Charles R Greathouse IV, Sep 01 2015

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

J. Pintz, A note on Romanov's constant, Acta Mathematica Hungarica 112:1-2 (2006), pp. 1-14.

PROG

(Haskell)

a081310 n = a081310_list !! (n-1)

a081310_list = filter ((== 0) . a081308) [1..]

-- Reinhard Zumkeller, Jul 04 2012

(PARI) is(n)=for(i=0, logint(n, 3), my(k=3^i); while(k<n, if(isprime(n-k), return(1)); k<<=1)); 0 \\ Charles R Greathouse IV, Sep 01 2015

CROSSREFS

A118955 is a subsequence.

Union of A081312 and A081313.

Cf. A000040, A003586.

Sequence in context: A009056 A065475 A062983 * A053233 A121818 A179005

Adjacent sequences:  A081308 A081309 A081310 * A081312 A081313 A081314

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 17 2003

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 25 14:47 EST 2020. Contains 338625 sequences. (Running on oeis4.)