A257786 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.

0, 1, 27, 376, 13131, 234595324075, 54377519037479592374299, 8326623359858152426050700, 1513868951125582592290131113769528

Offset

1,3

Comments

It appears that this sequence is finite.

Links

Table of n, a(n) for n=1..9.

Example

376 = sqrt(3+7+6)*(3^2+7^2+6^2).
13131 = sqrt(1+3+1+3+1)*(1^7+3^7+1^7+3^7+1^7).

Prog

(Python)
def moda(n, a):
....kk = 0
....while n > 0:
........kk= kk+(n%10)**a
........n =int(n//10)
....return kk
def sod(n):
....kk = 0
....while n > 0:
........k= kk+(n%10)
........n =int(n//10)
....return kk
for a in range (1, 10):
    for c in range (1, 10**8):
        if c**2==sod(c)*moda(c, a)**2:
            print (a, c, sod(c), moda(c, a))

Crossrefs

Cf. A028839, A061209, A115518, A130680.

Sequence in context: A042410 A110207 A223205 * A161530 A161954 A162369

Adjacent sequences: A257783 A257784 A257785 * A257787 A257788 A257789

Keyword

base,nonn,more

Author

Pieter Post, May 08 2015

Extensions

a(6) from Giovanni Resta, May 09 2015

a(7)-a(9) from Chai Wah Wu, Nov 29 2015

Status

approved