A063840 Numbers k such that sigma(k) - usigma(k) is a square and sets a new record for such squares.

1, 18, 28, 40, 84, 120, 208, 372, 424, 552, 624, 900, 1152, 1848, 2784, 3904, 4488, 4992, 7448, 7896, 9120, 11712, 13720, 14280, 19920, 22344, 26040, 27144, 37920, 41160, 52920, 88920, 107100, 132480, 186732, 195300, 208152, 240240, 243432

Offset

1,2

Links

Harry J. Smith, Table of n, a(n) for n = 1..100

Prog

(PARI) a=-1; u(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)); j=[];
for(n=1, 300000, x=sigma(n)-u(n); if(issquare(x), b=x; if(b>a, a=b; j=concat(j, n)))); j
(PARI) u(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d))
{ n=0; a=-1; for (m=1, 10^9, if(issquare(b=sigma(m) - u(m)), if(b>a, a=b; write("b063840.txt", n++, " ", m); if (n==100, break))) ) } \\ Harry J. Smith, Sep 01 2009

Crossrefs

Cf. A048146.

Sequence in context: A363659 A216259 A117101 * A180117 A339633 A167333

Adjacent sequences: A063837 A063838 A063839 * A063841 A063842 A063843

Keyword

nonn

Author

Jason Earls, Aug 25 2001

Status

approved