OFFSET
1,2
LINKS
Vighnesh Patil, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = sqrt(A118547(n)). - Michel Marcus, Jul 07 2025
EXAMPLE
15 is a term 15^2 = 225; digit sum of 225 = 2 + 2 + 5 = 9; 225 mod 9 = 0, so 15 is included.
18 is a term 18^2 = 324; digit sum of 324 = 3 + 2 + 4 = 9; 324 mod 9 = 0, so 16 is included.
MAPLE
digitSum := n -> add(i, i=convert(n, base, 10)):
isok := n -> modp(n^2, digitSum(n^2)) = 0:
select(isok, [$1..400])[];
MATHEMATICA
DigitSum[n_] := Total[IntegerDigits[n]];
Select[Range[400], Mod[#^2, DigitSum[#^2]] == 0 &]
PROG
(Python)
def digit_sum(n): return sum(int(d) for d in str(n))
def ok(n): return (n**2) % digit_sum(n**2) == 0
print([n for n in range(1, 1000) if ok(n)])
(PARI) isok(k) = (k^2 % sumdigits(k^2)) == 0; \\ Michel Marcus, Jul 06 2025
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Vighnesh Patil, Jul 06 2025
STATUS
approved
