A217704 Smallest number k > n for which sigma(k-n) = sigma(k+n).

34, 53, 23, 19, 26, 41, 31, 38, 49, 52, 68, 82, 112, 80, 103, 76, 110, 123, 166, 83, 101, 136, 219, 164, 130, 186, 147, 133, 381, 254, 208, 149, 253, 169, 131, 246, 172, 332, 404, 166, 245, 312, 148, 209, 309, 241, 487, 328, 217, 260

Offset: 1

Author

Jayanta Basu, Mar 26 2013

Keywords

• nonn

Comments

The sigma() in the definition is the sum-of-divisors function A000203.

Examples

			a(26)=186 because sigma(186-26)=sigma(160)=378=sigma(212)=sigma(186+26) and there is no k such that 26<k<186 for which sigma(k-26)=sigma(k+26).
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A217768.

Programs

Mathematica

Table[Min[Select[Range[500],DivisorSigma[1, # - n] == DivisorSigma[1, # + n] && # > n &]], {n,50}]

PARI

a(n)={my(k=n+1); while(sigma(k-n)<>sigma(k+n), k++); k} \\ Andrew Howroyd, Feb 25 2018