|
%I #16 Jun 18 2015 04:02:22
%S 25,32,46,56,70,88,92,98,100,113,121,130,145,146,152,175,176,182,185,
%T 206,209,212,218,227,236,239,244,248,274,293,295,301,316,317,320,323,
%U 331,338,350,352,355,362,377,386,394,397,398,406,409,413,439
%N Integers n such that both n and prime(n) have the same digital root.
%C Integers n such that A010888(n) = A038194(n).
%C Conjecture: a(n) ~ 9n. - _Charles R Greathouse IV_, Jun 17 2015
%H Charles R Greathouse IV, <a href="/A258876/b258876.txt">Table of n, a(n) for n = 1..10000</a>
%e Both 25 and prime(25) = 97 have 7 for a digital root.
%e Both 32 and prime(32) = 131 have 5 for a digital root.
%t Reap[Do[If[FixedPoint[Total[IntegerDigits[#]] &, n] == Mod[Prime[n], 9], Sow[n]], {n, 439}]][[2, 1]] (* Seidov *)
%t Select[Range[500], Mod[#, 9] == Mod[Prime[#], 9] &] (* _Alonso del Arte_, Jun 17 2015 *)
%o (PARI) isok(n) = (n % 9) == (prime(n) % 9); \\ _Michel Marcus_, Jun 17 2015
%o (PARI) n=0; forprime(p=2,1e4, if((p-n++)%9==0, print1(n", "))) \\ _Charles R Greathouse IV_, Jun 17 2015
%Y Cf. A010888, A038194.
%K base,nonn
%O 1,1
%A _Zak Seidov_, Jun 13 2015
|
