A074242 Numbers n such that sigma(n+1) = reverse(sigma(n)).

5602, 42346, 184650339, 356930335, 453038125082

Offset: 1

Author

Joseph L. Pe, Sep 19 2002

Keywords

• base
• more
• nonn

Comments

a(6) > 10^13. - Giovanni Resta, Jun 26 2015

Examples

			sigma(5602 + 1) = 6048 = reverse(8406) = reverse(sigma(5602)), so 5602 is a term of the sequence.
		

Crossrefs

Cf. A028980 (sigma(n) = reverse(sigma(n))).

Programs

Mathematica

Do[ If[FromDigits[Reverse[IntegerDigits[DivisorSigma[1, n]]]] == DivisorSigma[1, n + 1], Print[n]], {n, 1, 10^7}]

PARI

isok(n) = digits(sigma(n+1)) == Vecrev(digits(sigma(n))); \\ Michel Marcus, Jun 26 2015

Extensions

a(3)-a(4) from Donovan Johnson, Feb 01 2009

a(5) from Giovanni Resta, Jun 26 2015