A079026 Numbers that can be represented as 2*p + 3*q, where p and q are prime.

10, 12, 13, 15, 16, 19, 20, 21, 23, 25, 27, 28, 29, 31, 32, 35, 37, 39, 40, 41, 43, 44, 45, 47, 49, 52, 53, 55, 57, 59, 61, 63, 64, 65, 67, 68, 71, 73, 75, 77, 79, 80, 83, 85, 88, 89, 91, 92, 93, 95, 97, 99, 100, 101, 103, 107, 109, 112, 113, 115, 117, 119, 121, 124, 125, 127

Offset

1,1

Comments

The primes p and q may be the same.

Links

Zak Seidov, Table of n, a(n) for n = 1..1000

Formula

a(n) = 2*p + 3*q, for some primes p and q.

a(n) > 3n + O(n/log n). - Charles R Greathouse IV, Dec 04 2012

Example

13 = 2*2 + 3*3, with p = 2 and q = 3.

Mathematica

mx = 130; Union@ Flatten@ Table[ 2Prime[i] + 3Prime[j], {i, PrimePi[mx/2]}, {j, PrimePi[(mx - 2Prime[i])/3]}] (* Robert G. Wilson v, Dec 12 2012 *)

Prog

(PARI) for(i=1, 200, for(j=1, i/2, k=floor((i-2*j)/3); if(i-2*j-3*k, if(isprime(j), if(isprime(k), print(i); break, )))))
(PARI) list(lim)=my(v=vectorsmall(lim\1), u=List()); forprime(p=2, lim\2, forprime(q=2, (lim-2*p)\3, v[2*p+3*q]=1)); for(i=1, #v, if(v[i], listput(u, i))); Vec(u) \\ Charles R Greathouse IV, Dec 03 2012

Crossrefs

Sequence in context: A124404 A031288 A127957 * A219956 A331276 A230597

Adjacent sequences: A079023 A079024 A079025 * A079027 A079028 A079029

Keyword

easy,nonn

Author

Randy L. Ekl, Feb 01 2003

Extensions

Missing term, 100 (equal to 2 * 47 + 3 * 2), added by Zak Seidov, Dec 02 2012

Status

approved