OFFSET
1,1
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1995 (terms < 10^16)
EXAMPLE
31 = sigma(4^2) = sigma(5^2); 187131 = sigma(326^2) = sigma(407^2); etc.
PROG
(PARI) m=10^5; m2=m^2; s=vector(m); ss=vector(m); v=vector(49); for(j=1, m, s[j]=sigma(j^2)); ss=vecsort(s); c=0; for(j=2, m, if(s[j]>m2, next); if(s[j]>=ss[j], for(k=j, m-1, if(s[j]==ss[k], if(s[j]<>ss[k+1], next(2)); k=m-1)), forstep(k=j-1, 2, -1, if(s[j]==ss[k], if(s[j]<>ss[k-1], next(2)); k=2))); for(k=j+1, m, if(s[j]==s[k], if(gcd(j, k)==1, c++; v[c]=s[j])))); v=vecsort(v); n=0; for(j=2, 49, if(v[j-1]<>v[j], n++; print(n " " v[j]))) /* Donovan Johnson, Apr 20 2013 */
CROSSREFS
KEYWORD
nonn
AUTHOR
David W. Wilson, Jan 04 2001
STATUS
approved