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A080196 13-smooth numbers which are not 11-smooth. 4
13, 26, 39, 52, 65, 78, 91, 104, 117, 130, 143, 156, 169, 182, 195, 208, 234, 260, 273, 286, 312, 325, 338, 351, 364, 390, 416, 429, 455, 468, 507, 520, 546, 572, 585, 624, 637, 650, 676, 702, 715, 728, 780, 819, 832, 845, 858, 910, 936, 975, 1001, 1014, 1040 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Numbers of the form 2^r*3^s*5^t*7^u*11^v*13^w with r, s, t, u, v >= 0, w > 0.
LINKS
FORMULA
From Amiram Eldar, Nov 10 2020: (Start)
a(n) = 13 * A080197(n).
Sum_{n>=1} 1/a(n) = 77/192. (End)
EXAMPLE
78 = 2*3*13 is a term but 77 = 7*11 is not.
MATHEMATICA
Select[Range[1000], FactorInteger[#][[-1, 1]] == 13 &] (* Amiram Eldar, Nov 10 2020 *)
PROG
(PARI) {m=1040; z=[]; for(r=0, floor(log(m)/log(2)), a=2^r; for(s=0, floor(log(m/a)/log(3)), b=a*3^s; for(t=0, floor(log(m/b)/log(5)), c=b*5^t; for(u=0, floor(log(m/c)/log(7)), d=c*7^u; for(v=0, floor(log(m/d)/log(11)), e=d*11^v; for(w=1, floor(log(m/e)/log(13)), z=concat(z, e*13^w))))))); z=vecsort(z); for(i=1, length(z), print1(z[i], ", "))}
CROSSREFS
Sequence in context: A044898 A048842 A008595 * A033025 A044838 A033010
KEYWORD
easy,nonn
AUTHOR
Klaus Brockhaus, Feb 10 2003
STATUS
approved

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Last modified February 21 04:08 EST 2024. Contains 370219 sequences. (Running on oeis4.)