A070299 Numbers n such that sigma(n+x) = sigma(n-x) for some 0 < x < n.

19, 23, 26, 31, 34, 38, 40, 41, 49, 52, 53, 55, 61, 63, 68, 69, 73, 74, 75, 76, 80, 82, 83, 85, 91, 96, 101, 103, 104, 106, 110, 112, 113, 117, 122, 123, 126, 130, 131, 133, 136, 145, 146, 147, 148, 149, 151, 152, 155, 156, 157, 158, 160, 161, 162, 163, 164, 166

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Mathematica

nsQ[n_]:=Total[Boole[Table[DivisorSigma[1, n+x]==DivisorSigma[1, n-x], {x, n-1}]]]>0; Select[Range[200], nsQ] (* Harvey P. Dale, Mar 19 2019 *)

Prog

(PARI) for(n=1, 200, if(0<sum(i=1, n-1, if(sigma(n+i)-sigma(n-i), 0, 1)), print1(n, ", ")))
(PARI) is(n)=forcomposite(c=15, n-1, if(sigma(c)==sigma(2*n-c), return(1))); 0 \\ Charles R Greathouse IV, Nov 06 2014

Crossrefs

Sequence in context: A343740 A317254 A226687 * A159021 A100460 A166061

Adjacent sequences: A070296 A070297 A070298 * A070300 A070301 A070302

Keyword

nonn

Author

Benoit Cloitre, May 10 2002

Status

approved