The On-Line Encyclopedia of Integer Sequences (OEIS)

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A193226

Least semiprime whose sum of prime factors equals 2^n.
(history; published version)

#10 by Charles R Greathouse IV at Mon May 13 01:54:20 EDT 2013

LINKS

_Charles R Greathouse IV_, , <a href="/A193226/b193226.txt">Table of n, a(n) for n = 2..1000</a>

Discussion

Mon May 13

01:54

OEIS Server: https://oeis.org/edit/global/1915

#9 by Charles R Greathouse IV at Mon May 13 01:49:41 EDT 2013

LINKS

_Charles R Greathouse IV, _, <a href="/A193226/b193226.txt">Table of n, a(n) for n = 2..1000</a>

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

Discussion

Mon May 13

01:49

OEIS Server: https://oeis.org/edit/global/1914

#8 by Russ Cox at Fri Mar 30 18:35:55 EDT 2012

AUTHOR

_Michel Lagneau (mn.lagneau2(AT)orange.fr), _, Jul 18 2011

Discussion

Fri Mar 30

18:35

OEIS Server: https://oeis.org/edit/global/205

#7 by T. D. Noe at Mon Aug 01 00:16:29 EDT 2011

STATUS

proposed

approved

#6 by Charles R Greathouse IV at Sun Jul 31 19:38:12 EDT 2011

STATUS

editing

proposed

#5 by Charles R Greathouse IV at Sun Jul 31 19:37:55 EDT 2011

LINKS

Charles R Greathouse IV, <a href="/A193226/b193226.txt">Table of n, a(n) for n = 2..1000</a>

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

STATUS

approved

editing

#4 by T. D. Noe at Tue Jul 19 12:07:01 EDT 2011

STATUS

proposed

approved

#3 by Michel Lagneau at Mon Jul 18 12:15:17 EDT 2011

STATUS

editing

proposed

#2 by Michel Lagneau at Mon Jul 18 12:14:48 EDT 2011

NAME

allocated for Michel LagneauLeast semiprime whose sum of prime factors equals 2^n.

DATA

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

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:

CROSSREFS

Cf. A001358.

KEYWORD

allocated

nonn

AUTHOR

Michel Lagneau (mn.lagneau2(AT)orange.fr), Jul 18 2011

STATUS

approved

editing

#1 by Michel Lagneau at Mon Jul 18 12:14:48 EDT 2011

NAME

allocated for Michel Lagneau

KEYWORD

allocated

STATUS

approved