A162948 Numbers with a sum of digits equal to their smallest prime factor.

2, 3, 5, 7, 20, 21, 110, 111, 133, 200, 201, 209, 247, 407, 481, 511, 629, 803, 1010, 1011, 1100, 1101, 1141, 1387, 1417, 1651, 1679, 1853, 2000, 2001, 2023, 2119, 2159, 2353, 2401, 2771, 3031, 3077, 3097, 3383, 3439, 3523, 3749, 3781, 4577, 4607, 4913, 5149, 5161

Offset

1,1

Links

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

Formula

{n: A007953(n) = A020639(n)}. - R. J. Mathar, Jul 19 2009

Example

133 is in the sequence because 1 + 3 + 3 = 7 and 7 is the smallest prime factor of 133.

Maple

A007953 := proc(n) local d; add(d, d=convert(n, base, 10)) ; end:
A020639 := proc(n) min(op(numtheory[factorset](n) )) ; end:
isA162948 := proc(n) RETURN( A007953(n) = A020639(n)) ; end:
for n from 1 to 6000 do if isA162948(n) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Jul 19 2009

Crossrefs

Cf: A007953, A020639.

Even terms: A069537.

Sequence in context: A110457 A320584 A209191 * A024768 A024769 A340112

Adjacent sequences: A162945 A162946 A162947 * A162949 A162950 A162951

Keyword

nonn,base

Author

Claudio Meller, Jul 18 2009

Extensions

Single-digit primes added by R. J. Mathar, Jul 19 2009

Status

approved