A232540 - OEIS

A232540

Numbers n such that (n(n+1)/2) modulo sigma(n) = 1.

10, 22, 34, 46, 58, 82, 94, 106, 118, 142, 166, 178, 202, 214, 226, 262, 274, 298, 334, 346, 358, 382, 385, 394, 430, 454, 466, 478, 502, 514, 526, 538, 562, 586, 622, 634, 694, 706, 718, 766, 778, 802, 838, 862, 886, 898, 922, 934, 958, 982, 1006, 1018, 1042

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OFFSET

1,1

COMMENTS

Also numbers n such that antisigma(n) modulo sigma(n) = 1. Antisigma(n) = A024816(n) = the sum of the nondivisors of n that are between 1 and n, sigma(n) = A000203(n) = the sum of the divisors of n.

Numbers n such that A232324(n) = 1.

Number 5950 is only squareful number from first 1400 terms (< 50000) of this sequence.

Conjecture: supersequence of A112774 (semiprimes of the form 6n+4).

LINKS

Jaroslav Krizek, Table of n, a(n) for n = 1..1000

EXAMPLE

106 is in sequence because antisigma(106) mod sigma(106) = 5509 mod 162 = 1.

MATHEMATICA

Select[Range[1100], Mod[(#(#+1))/2, DivisorSigma[1, #]]==1&] (* Harvey P. Dale, Sep 08 2017 *)

CROSSREFS

Cf. A000203, A076617, A024816, A112774, A232324, A232538.

Sequence in context: A179887 A339003 A017641 * A217573 A276626 A211482

Adjacent sequences: A232537 A232538 A232539 * A232541 A232542 A232543

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Nov 25 2013

STATUS

approved