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 A242963 Numbers n such that A242962(n) = sigma(n) = A000203(n). 5
 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A242962(n) = (n*(n+1)/2) mod antisigma(n) = A000217(n) mod A024816(n). Union of number 5 and numbers >= 7. Conjecture: this sequence lists all the positive integers n such that, for some integer k, (sin(k*Pi/n))^2 is irrational. - Lorenzo Sauras Altuzarra, Jan 27 2020 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..14995 MATHEMATICA Select[Range[3, 71], DivisorSigma[1, #] == Mod[PolygonalNumber@ #, Total@ Complement[Range@ #, Divisors@ #]] &] (* Michael De Vlieger, Jan 28 2020 *) PROG (MAGMA) [n: n in [3..100000] | ((n*(n+1)div 2) mod (n*(n+1)div 2-SumOfDivisors(n))) eq (SumOfDivisors(n))] CROSSREFS Cf. A000203, A000217, A002961, A024816, A242962, A243117, A243118, A217290, A009005. Sequence in context: A068001 A213443 A302980 * A191846 A068213 A065966 Adjacent sequences:  A242960 A242961 A242962 * A242964 A242965 A242966 KEYWORD nonn AUTHOR Jaroslav Krizek, May 29 2014 STATUS approved

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Last modified June 16 02:14 EDT 2021. Contains 345055 sequences. (Running on oeis4.)