A069822 Numbers k for which there is at least one x < k such that sigma(x) = sigma(k).
11, 15, 17, 23, 25, 26, 31, 35, 38, 39, 41, 46, 47, 51, 53, 55, 56, 58, 59, 62, 65, 69, 70, 71, 75, 77, 78, 79, 82, 83, 87, 89, 92, 94, 95, 97, 103, 107, 110, 113, 115, 116, 118, 119, 122, 123, 124, 125, 127, 130, 131, 135, 139, 140, 141, 142, 143, 145, 151, 153
Offset: 1
Links
- Antti Karttunen, Table of n, a(n) for n = 1..10547
- Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
Programs
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PARI
for(s=1,200,if(prod(i=1,s-1, sigma(i)-sigma(s))==0,print1(s,",")))
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PARI
for(n=1,16384,y=0;s=sigma(n);for(k=1,(n-1),if(sigma(k)==s,y=1;break)); if(y,i++;write("b069822.txt", i," ", n))); \\ Antti Karttunen, Dec 08 2017 -
PARI
is(k) = invsigmaMin(sigma(k)) < k; \\ Amiram Eldar, Dec 20 2024, using Max Alekseyev's invphi.gp
Comments