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A058075 Numbers n such that GCD(sigma(n), sigma(n+1)) = 1, where sigma(n) is sum of positive divisors of n. 4
1, 2, 3, 4, 7, 8, 9, 15, 16, 18, 24, 25, 31, 35, 36, 48, 63, 64, 72, 80, 81, 97, 99, 100, 120, 121, 127, 128, 143, 144, 162, 200, 224, 225, 241, 255, 256, 288, 289, 323, 337, 399, 400, 483, 511, 512, 528, 529, 575, 576, 577, 578, 624, 625, 675, 721, 722, 728, 729 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..3000

EXAMPLE

8 is included because sigma(8) = 15 is relatively prime to sigma(9) = 13.

MATHEMATICA

Select[Range@800, GCD @@ DivisorSigma[1, {#, # + 1}] == 1 &] (* Ivan Neretin, Jan 27 2017 *)

PROG

(PARI) lista(nn) = {for(n=1, nn, if (gcd(sigma(n), sigma(n+1)) == 1, print1(n, ", "))); } \\ Michel Marcus, May 19 2014

CROSSREFS

Cf. A058074.

Sequence in context: A050271 A322742 A152037 * A243495 A029783 A112736

Adjacent sequences:  A058072 A058073 A058074 * A058076 A058077 A058078

KEYWORD

nonn

AUTHOR

Leroy Quet, Nov 11 2000

STATUS

approved

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Last modified January 16 23:44 EST 2019. Contains 319206 sequences. (Running on oeis4.)