A257786 - OEIS

%I #15 Nov 29 2015 21:30:58

%S 0,1,27,376,13131,234595324075,54377519037479592374299,

%T 8326623359858152426050700,1513868951125582592290131113769528

%N Numbers n such that the square root of the sum of the digits times the sum of the digits of n in some power equal n.

%C It appears that this sequence is finite.

%e 376 = sqrt(3+7+6)*(3^2+7^2+6^2).

%e 13131 = sqrt(1+3+1+3+1)*(1^7+3^7+1^7+3^7+1^7).

%o (Python)

%o def moda(n,a):

%o ....kk = 0

%o ....while n > 0:

%o ........kk= kk+(n%10)**a

%o ........n =int(n//10)

%o ....return kk

%o def sod(n):

%o ....kk = 0

%o ....while n > 0:

%o ........k= kk+(n%10)

%o ........n =int(n//10)

%o ....return kk

%o for a in range (1, 10):

%o     for c in range (1, 10**8):

%o         if c**2==sod(c)*moda(c,a)**2:

%o             print (a,c, sod(c),moda(c,a))

%Y Cf. A028839, A061209, A115518, A130680.

%K base,nonn,more

%O 1,3

%A _Pieter Post_, May 08 2015

%E a(6) from _Giovanni Resta_, May 09 2015

%E a(7)-a(9) from _Chai Wah Wu_, Nov 29 2015