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A231546
Numbers k such that sigma(k) = sigma(k-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
OFFSET
1,1
COMMENTS
Also, numbers k such that k = antisigma(k) - antisigma(k-1), where antisigma(k) = A024816(k) = the sum of the non-divisors of k that are between 1 and k.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10135 (calculated using the b-file at A002961; terms 1..550 from Hugo Pfoertner)
FORMULA
a(n) = A002961(n) + 1.
EXAMPLE
15 = antisigma(15) - antisigma(14) = 96 - 81.
MATHEMATICA
SequencePosition[DivisorSigma[1, Range[210000]], {x_, x_}][[;; , 2]] (* Harvey P. Dale, May 28 2024 *)
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 * A362809 A063906 A194481
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Nov 11 2013
EXTENSIONS
More terms from Hugo Pfoertner, Mar 06 2020
STATUS
approved