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Semiprimes n such that n + 1 is divisible by the sum of decimal digits of n.
2

%I #6 Sep 16 2015 12:51:45

%S 10,14,34,65,143,215,299,362,454,458,545,655,671,689,799,917,922,923,

%T 943,1003,1007,1042,1055,1111,1154,1199,1253,1273,1379,1507,1529,1739,

%U 1807,1835,1919,1957,2045,2095,2183,2209,2231,2279,2302,2326,2342,2435

%N Semiprimes n such that n + 1 is divisible by the sum of decimal digits of n.

%e 14 and 15 are semiprimes. 14+1 = 15 is divisible by 1+4 = 5, hence 14 is in the sequence; 15+1 = 16 is not divisible by 1+5 = 6, hence 15 is not in the sequence. - _Klaus Brockhaus_, Sep 29 2008

%t Select[Range[5000], Sum[FactorInteger[ # ][[i, 2]], {i, 1, Length[FactorInteger[ # ]]}] == 2 && Mod[ # + 1, Plus @@ IntegerDigits[ # ]] == 0 &] (* _Stefan Steinerberger_, Sep 29 2008 *)

%Y Cf. A001358 (semiprimes). - _Klaus Brockhaus_, Sep 29 2008

%K base,nonn

%O 1,1

%A _Giovanni Teofilatto_, Sep 27 2008

%E Corrected and extended by _Stefan Steinerberger_ and _Klaus Brockhaus_, Sep 29 2008