cp's OEIS Frontend

A323050 Numbers that cannot be written as a sum of two or fewer 7-smooth numbers (A002473).

%I A323050 #15 Feb 14 2019 12:34:25
%S A323050 311,479,551,619,622,671,719,839,851,933,937,958,1102,1103,1117,1151,
%T A323050 1193,1238,1244,1291,1319,1342,1391,1433,1437,1438,1487,1499,1511,
%U A323050 1531,1553,1555,1559,1619,1651,1653,1667,1678,1679,1697,1857,1866,1871,1874,1913,1916,1919,1933,1937,1991,2011,2013,2077,2113,2117,2157
%N A323050 Numbers that cannot be written as a sum of two or fewer 7-smooth numbers (A002473).
%C A323050 Numbers that are not of the form (2^i * 3^j * 5^k * 7^l)*a + (2^m * 3^n * 5^p * 7^q)*b, with i,j,k,m,n,p >= 0, and a,b = 0 or 1. The first number excluded is 311.
%C A323050 These numbers are also included in A323046 and A323049.
%t A323050 f[n_] := Union@Flatten@Table[2^a*3^b*5^c*7^d, {a, 0, Log2[n]}, {b, 0, Log[3, n/2^a]}, {c, 0, Log[5, n/(2^a*3^b)]}, {d, 0, Log[7, n/(2^a*3^b*5^c)]}];
%t A323050 b = Block[{nn = 3000, s}, s = f[nn]; {0, 1}~Join~Select[Union@Flatten@Outer[Plus, s, s], # <= nn &]];
%t A323050 Complement[Range[3000], b]
%Y A323050 Similar to A323046 (for 3-smooth) and A323049 (for 5-smooth). Cf. A002473.
%K A323050 nonn
%O A323050 1,1
%A A323050 _Carlos Alves_, Jan 03 2019