The OEIS is supported by the many generous donors to the OEIS Foundation.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #9 Feb 15 2015 01:07:50
%S 1,2,3,4,5,6,7,8,9,10,20,22,30,39,40,50,60,70,80,88,90,93,100,101,102,
%T 103,104,105,106,107,108,109,110,120,123,130,132,140,144,150,160,170,
%U 180,189,190,198,200,201,202,203,204,205,206,207,208,209,210,213,220
%N Numbers with property that the digital sum times the product of the digits is a square.
%C 93 is in the list because (9+3)*(9*3) = 12*27 = 324 = 18^2.
%p a := proc (n) local nn, L: nn := convert(n, base, 10): L := nops(nn): if type(sqrt(add(nn[i], i = 1 .. L)*(product(nn[i], i = 1 .. L))), integer) = true then n else end if end proc: seq(a(n), n = 1 .. 220); # _Emeric Deutsch_, Jun 27 2009
%o (PARI) isok(n) = my(d=digits(n)); issquare(sumdigits(n)*prod(k=1,#d,d[k])); \\ _Michel Marcus_, Feb 14 2015
%Y Cf. A007953 (sum of digits), A007954 (product of digits).
%K nonn,base
%O 1,2
%A _Claudio Meller_, Jun 07 2009