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A059113 Numbers which are the sum of the divisors of two distinct coprime squares. 1
31, 187131, 347529, 658749, 2106853, 3969147, 4657471, 4980801, 6540807, 10185273, 20421219, 25690413, 42827421, 44136183, 51598911, 73854183, 202765017, 299457613, 307464339, 308953281, 314858271, 504081669, 516979281, 600877641, 613602549 (list; graph; refs; listen; history; text; internal format)
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

Sequence in context: A117579 A249584 A107122 * A057839 A123524 A123523

Adjacent sequences:  A059110 A059111 A059112 * A059114 A059115 A059116

KEYWORD

nonn

AUTHOR

David W. Wilson, Jan 04 2001

STATUS

approved

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Last modified October 17 21:34 EDT 2019. Contains 328133 sequences. (Running on oeis4.)