OFFSET
1,1
COMMENTS
Semiprimes in A059094.
No a(n) have digit sum 27, because numbers with digit sum divisible by 9 are divisible by 9 and thus not semiprimes. The first member of the sequence with digit sum > 8 is 28999999 = a(1006). - Robert Israel, Jul 10 2014
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..1000
EXAMPLE
35 is in the sequence because 35 = 5 * 7 which is semiprime. Also, (3 + 5) = 8 = 2^3.
1043 is in the sequence because 1043 = 7 * 149 which is semiprime. Also, (1 + 0 + 4 + 3) = 8 = 2^3.
MAPLE
N:= 10000: # to get all terms up to N
maxj:= floor((9*(1+ilog10(N)))^(1/3)):
cubes:= {seq(j^3, j=1..maxj)}:
filter:= proc(n)
local s;
if numtheory:-bigomega(n) <> 2 then return false fi;
s:= convert(convert(n, base, 10), `+`);
member(s, cubes);
end proc:
select(filter, [$1..N]); # Robert Israel, Jul 10 2014
MATHEMATICA
sppcQ[n_]:=PrimeOmega[n]==2&&IntegerQ[Surd[Total[IntegerDigits[n]], 3]]; Select[Range[5200], sppcQ] (* Harvey P. Dale, Apr 07 2017 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
K. D. Bajpai, Jul 09 2014
STATUS
approved