

A323050


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


3



311, 479, 551, 619, 622, 671, 719, 839, 851, 933, 937, 958, 1102, 1103, 1117, 1151, 1193, 1238, 1244, 1291, 1319, 1342, 1391, 1433, 1437, 1438, 1487, 1499, 1511, 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
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OFFSET

1,1


COMMENTS

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.
These numbers are also included in A323046 and A323049.


LINKS

Table of n, a(n) for n=1..56.


MATHEMATICA

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)]}];
b = Block[{nn = 3000, s}, s = f[nn]; {0, 1}~Join~Select[Union@Flatten@Outer[Plus, s, s], # <= nn &]];
Complement[Range[3000], b]


CROSSREFS

Similar to A323046 (for 3smooth) and A323049 (for 5smooth). Cf. A002473.
Sequence in context: A259221 A142626 A142950 * A104718 A142576 A025024
Adjacent sequences: A323047 A323048 A323049 * A323051 A323052 A323053


KEYWORD

nonn


AUTHOR

Carlos Alves, Jan 03 2019


STATUS

approved



