A217390 Numbers n such that sum of squares of digits of n equals the sum of prime divisors of n.

12, 581, 1014, 1036, 1180, 1272, 1746, 2553, 3420, 3741, 4140, 4544, 5104, 5238, 5313, 5966, 7134, 7272, 8174, 8346, 8549, 9153, 9525, 9536, 10476, 11070, 11800, 12350, 12882, 13481, 13702, 14045, 15341, 15974, 16415, 16999, 17051, 17220, 17444, 18361, 18798

Offset: 1

Author

Michel Lagneau, Oct 05 2012

Keywords

• nonn
• easy
• base

Comments

n such that A003132(n) = A008472(n).

Examples

			581 =  7*83 is in the sequence because 5^2 + 8^2 + 1^2 = 7 + 83 = 90.
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A003132, A008472.

Programs

Maple

with(numtheory):A:= proc(n) add(u^2, u=convert(n, base, 10)) ; end proc: for i from 2 to 20000 do:x:=factorset(i):n1:=nops(x): s:=sum('x[i] ', 'i'=1..n1):if s=A(i) then printf(`%d, `,i):else fi:od:

Mathematica

Rest[Select[Range[20000], Total[Transpose[FactorInteger[#]][[1]]]==Total[IntegerDigits[#]^2]&]]

PARI

ok(n)={vecsum(factor(n)[, 1]) == vecsum(apply(d->d^2, digits(n)))} \\ Andrew Howroyd, Feb 25 2018