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A231546 Numbers n such that sigma(n) = sigma(n-1). 8
15, 207, 958, 1335, 1365, 1635, 2686, 2975, 4365, 14842, 18874, 19359, 20146, 24958, 33999, 36567, 42819, 56565, 64666, 74919, 79827, 79834, 84135, 92686, 109215, 111507, 116938, 122074, 138238, 147455, 161002, 162603, 166935, 174718, 190774, 193894, 201598 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also, numbers n such that n = antisigma(n) - antisigma(n-1), where antisigma(n) = A024816(n) = the sum of the non-divisors of n that are between 1 and n.

LINKS

Hugo Pfoertner, Table of n, a(n) for n = 1..550

FORMULA

a(n) = A002961(n) + 1.

EXAMPLE

15 = antisigma(15) - antisigma(14) = 96 - 81.

PROG

(PARI) n=0; sp=sigma(2); for(k=3, oo, my(s=sigma(k)); if(s==sp, print1(k, ", "); n++; if(n>36, break)); sp=s) \\ Hugo Pfoertner, Mar 06 2020

CROSSREFS

Cf. A002961, A024816 (antisigma(n)), A231545 (numbers n such that antisigma(n) = antisigma(n-1)).

Sequence in context: A075280 A093747 A061637 * A063906 A194481 A078265

Adjacent sequences:  A231543 A231544 A231545 * A231547 A231548 A231549

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Nov 11 2013

EXTENSIONS

More terms from Hugo Pfoertner, Mar 06 2020

STATUS

approved

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Last modified November 24 01:40 EST 2020. Contains 338603 sequences. (Running on oeis4.)