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A245021 Semiprimes whose digit sum is a perfect cube. 1
10, 26, 35, 62, 134, 143, 161, 206, 215, 305, 314, 323, 341, 413, 422, 611, 1007, 1043, 1115, 1133, 1142, 1205, 1214, 1241, 1313, 1322, 1403, 1502, 2033, 2042, 2051, 2105, 2123, 2231, 2321, 2402, 2501, 3005, 3113, 3131, 3401, 4022, 4031, 4103, 4121, 5102, 5111 (list; graph; refs; listen; history; text; internal format)
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

Cf. A001358,  A007953, A059094.

Sequence in context: A005278 A157075 A262998 * A045039 A080059 A071348

Adjacent sequences:  A245018 A245019 A245020 * A245022 A245023 A245024

KEYWORD

nonn,base

AUTHOR

K. D. Bajpai, Jul 09 2014

STATUS

approved

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Last modified July 25 14:32 EDT 2017. Contains 289795 sequences.