A199980 Primes whose multiplicative digital root is 2.

2, 37, 43, 73, 137, 173, 211, 223, 317, 367, 389, 431, 673, 827, 839, 929, 983, 1223, 1279, 1297, 1367, 1447, 1621, 1637, 1693, 1999, 2111, 2161, 2179, 2213, 2269, 2339, 2393, 2663, 2699, 2719, 2791, 2917, 2969, 2971, 3167, 3169, 3221, 3329, 3463, 3499, 3617

Offset

1,1

Comments

Complement of A199981 with respect to A034049, numbers whose multiplicative digital root is 2.

Links

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

Example

Prime 389 is in sequence because 3*8*9=216, 2*1*6 =12, 1*2=2.

Maple

mdr:= proc(n) option remember;
  local t;
  t:= convert(convert(n, base, 10), `*`);
  if t < 10  then t else procname(t) fi
end proc:
select(t -> mdr(t) = 2 and isprime(t), [2, seq(i, i=3..10000, 2)]); # Robert Israel, Nov 05 2020

Mathematica

t = {}; n = 0; While[Length[t] < 100, n = NextPrime[n]; s = n; While[s >= 10, s = Times @@ IntegerDigits[s]]; If[s == 2, AppendTo[t, n]]]; t (* T. D. Noe, Nov 15 2011 *)
Select[Prime[Range[600]], FixedPoint[Times@@IntegerDigits[#]&, #]==2&] (* Harvey P. Dale, Mar 28 2012 *)

Crossrefs

Cf. A199981 (nonprime numbers whose multiplicative digital root is 2).

Includes A107612.

Cf. A031347, A034049.

Sequence in context: A066196 A107180 A162577 * A084548 A063999 A062606

Adjacent sequences: A199977 A199978 A199979 * A199981 A199982 A199983

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 13 2011

Status

approved