A275370 Odd numbers n such that sigma(n) = sigma(2*n-1).

1, 13545, 57645, 116865, 1440495, 7029855, 8596455, 27361125, 41100345, 48289185, 56122185, 77560065, 103225185, 134813385, 146591235, 163817745, 188358885, 198748305, 242668335, 269436375, 352094715, 358841385, 535135965, 563911335, 636719265, 712457655, 724692045

Offset: 1

Author

Altug Alkan, Jul 25 2016

Keywords

• nonn

Comments

The smallest term that is not divisible by 5 is 1577106531.

Examples

			The numbers n that solve sigma(n) = sigma(2n-1) are n = 1, 6, 348, 496, 1420, 1854, 4647, 5352, 6424, 13545, 21126,... The sequence selects the odd members.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..164 (terms < 2*10^11)

Crossrefs

Cf. A000203, A008438, A272553.

Programs

PARI

isok(n) = sigma(n) == sigma(2*n-1) && n % 2 == 1