OFFSET
1,2
COMMENTS
If a(n) has m = p^k digits, then a(n)*10^((p-1)*m) is also a member of the sequence. For instance, 1521*10^(2^k-4) is in the sequence for all integers k >=2. # Chai Wah Wu, Jun 08 2015
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..3730
FORMULA
a(n) = A153745(n)^2.
PROG
(Python)
from sympy import divisors
from gmpy2 import is_prime, isqrt, isqrt_rem, is_square
A258660_list = []
for l in range(1, 17):
....if not is_prime(l):
........fs = divisors(l)
........a, b = isqrt_rem(10**(l-1))
........if b > 0:
............a += 1
........for n in range(a, isqrt(10**l-1)+1):
............n2 = n**2
............ns = str(n2)
............for g in fs:
................y = 0
................for h in range(0, l, g):
....................y += int(ns[h:h+g])
................if not is_square(y):
....................break
............else:
................A258660_list.append(n2) # Chai Wah Wu, Jun 08 2015
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Doug Bell, Jun 06 2015
EXTENSIONS
Corrected a(13)-a(14) by Chai Wah Wu, Jun 08 2015
STATUS
approved