

A081311


Numbers that can be written as sum of a prime and an 3smooth 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
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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 112:12 (2006), pp. 114.


PROG

(Haskell)
a081310 n = a081310_list !! (n1)
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(nk), 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



