A217048 Semiprimes using only the curved digits 0, 3, 6, 8 and 9.

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

Robert Israel, Table of n, a(n) for n = 1..10000

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

Cf. A001358, A072960.

Sequence in context: A192425 A219687 A147415 * A105866 A267690 A084007

Adjacent sequences: A217045 A217046 A217047 * A217049 A217050 A217051

Keyword

nonn,base,easy

Author

Jonathan Vos Post, Sep 25 2012

Status

approved