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Numbers n such that digit sum of 2^n is less than or equal to n.
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%I #8 Sep 22 2019 08:40:15

%S 5,9,10,17,70

%N Numbers n such that digit sum of 2^n is less than or equal to n.

%C Probably there are no more terms.

%C Probably 5 and 70 are the only cases when digit sum of 2^n is equal to n. - Tanya Khovanova, Jul 23 2006

%C Probably 1, 2, 5 and 70 are the only cases when digit sum of 2^n is divisible by n. - Zak Seidov, Jul 24 2006

%t Select[Range[80],#>=Total[IntegerDigits[2^#]]&] (* _Harvey P. Dale_, Sep 22 2019 *)

%o (PARI) isok(n) = d = digits(2^n); sum(i=1, #d, d[i]) <= n; \\ _Michel Marcus_, Aug 17 2013

%Y Cf. A001370.

%K nonn,base,fini

%O 1,1

%A _Joshua Zucker_, Jul 24 2006