A052020 Sum of digits of k is a prime proper factor of k.

12, 20, 21, 30, 50, 70, 102, 110, 111, 120, 133, 140, 200, 201, 209, 210, 230, 247, 300, 308, 320, 322, 364, 407, 410, 476, 481, 500, 506, 511, 605, 629, 700, 704, 715, 782, 803, 832, 874, 902, 935, 1002, 1010, 1011, 1015, 1020, 1040, 1066, 1088, 1100, 1101

Offset

1,1

Comments

For each prime p there are infinitely many terms with sum of digits p. - Robert Israel, Feb 26 2017

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) local s;
  s:= convert(convert(n, base, 10), `+`);
  isprime(s) and (n mod s = 0)
end proc:
select(filter, [$10..10^4]); # Robert Israel, Feb 26 2017

Prog

(Python)
from sympy import isprime
def ok(n):
    sd = sum(map(int, str(n)))
    return 1 < sd < n and n%sd == 0 and isprime(sd)
print([k for k in range(1102) if ok(k)]) # Michael S. Branicky, Dec 20 2021

Crossrefs

Cf. A052018, A052019, A052021, A052022, A007953, A005349, A028834.

Sequence in context: A171795 A170806 A038528 * A075078 A050421 A307517

Adjacent sequences: A052017 A052018 A052019 * A052021 A052022 A052023

Keyword

nonn,base,easy

Author

Patrick De Geest, Nov 15 1999

Status

approved