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A199980
Primes whose multiplicative digital root is 2.
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
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.
Sequence in context: A066196 A107180 A162577 * A084548 A063999 A062606
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 13 2011
STATUS
approved