A193226 Least semiprime whose sum of prime factors equals 2^n.

4, 15, 39, 87, 183, 2071, 1255, 1527, 3063, 38551, 12279, 106327, 49143, 622231, 1113823, 1703767, 1310695, 9961111, 3145719, 39845527, 12582903, 310377127, 50331639, 2046816631, 335544295, 10603194271, 23890747663, 1610612727, 44023413103

Offset

2,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 2..1000

Example

a(10) = 3063 because 3063 = 3*1021, and 1021 + 3 = 2^10.

Maple

with(numtheory):for n from 1 to 30 do:x:=2^n:id:=0:for m from 1 to 10000 while(id=0) do:p:=ithprime(m):y:=x-p:if type(y, prime)=true then z:=y*p: id:=1:printf(`%d, `, z): else fi:od:od:

Prog

(PARI) a(n)=my(N=2^n); forprime(p=2, default(primelimit), if(isprime(N-p), return(p*(N-p)))) \\ Charles R Greathouse IV, Jul 31 2011

Crossrefs

Cf. A001358.

Sequence in context: A112666 A014629 A062486 * A291555 A336995 A053698

Adjacent sequences: A193223 A193224 A193225 * A193227 A193228 A193229

Keyword

nonn

Author

Michel Lagneau, Jul 18 2011

Status

approved