login
A217048
Semiprimes using only the curved digits 0, 3, 6, 8 and 9.
2
6, 9, 33, 38, 39, 69, 86, 93, 303, 309, 339, 386, 393, 398, 633, 669, 689, 698, 699, 803, 838, 866, 869, 886, 889, 893, 898, 899, 933, 939, 989, 993, 998, 3039, 3063, 3086, 3093, 3098, 3099, 3309, 3338, 3369, 3383, 3386, 3398, 3603, 3639, 3669, 3683, 3693
OFFSET
1,1
COMMENTS
This is to A079652 as semiprimes A001358 are to primes A000040.
LINKS
FORMULA
A001358 INTERSECTION A072960.
EXAMPLE
a(41) = 3338 = 2 * 1669, the 938th semiprime.
MAPLE
R:= [0, 3, 6, 8, 9]:
Res:= NULL: count:= 0:
for m from 1 while count < 100 do
L:= convert(m, base, 5);
n:= add(R[L[i]+1]*10^(i-1), i=1..nops(L));
if numtheory:-bigomega(n)=2 then Res:= Res, n; count:= count+1 fi
od:
Res; # Robert Israel, Feb 16 2020
PROG
(Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [n: n in [2..3700] | IsSemiprime(n) and Intseq(n) subset [0, 3, 6, 8, 9]]; // Bruno Berselli, Sep 25 2012
CROSSREFS
Sequence in context: A192425 A219687 A147415 * A105866 A267690 A084007
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Sep 25 2012
STATUS
approved