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A286359
Compound filter: a(n) = P(sigma(n), sigma(2n)), where P(n,k) is sequence A000027 used as a pairing function, and sigma is the sum of divisors (A000203).
4
4, 39, 109, 217, 259, 753, 473, 1005, 1288, 1729, 1093, 3769, 1499, 3105, 4489, 4309, 2503, 8295, 3101, 8557, 8033, 7057, 4489, 16713, 7534, 9633, 12601, 15281, 7051, 28513, 8033, 17829, 18193, 15985, 18193, 40561, 11363, 19761, 24809, 37765, 13903, 50817, 15269, 34537, 48283, 28513, 18193, 70249, 25708, 47679, 41113, 47069, 23059, 79521, 41113, 67281, 50801
OFFSET
1,1
LINKS
FORMULA
a(n) = (1/2)*(2 + ((A000203(n)+A000203(2*n))^2) - A000203(n) - 3*A000203(2*n)).
PROG
(PARI)
A000203(n) = sigma(n);
A286359(n) = (1/2)*(2 + ((A000203(n)+A000203(n+n))^2) - A000203(n) - 3*A000203(n+n));
for(n=1, 10000, write("b286359.txt", n, " ", A286359(n)));
(Scheme) (define (A286359 n) (* (/ 1 2) (+ (expt (+ (A000203 n) (A000203 (* 2 n))) 2) (- (A000203 n)) (- (* 3 (A000203 (* 2 n)))) 2)))
(Python)
from sympy import divisor_sigma as D
def T(n, m): return ((n + m)**2 - n - 3*m + 2)/2
def a(n): return T(D(n), D(2*n)) # Indranil Ghosh, May 12 2017
CROSSREFS
Cf. A000203, A002131, A054785 (sequences matching to this filter), also A161942, A286357.
Sequence in context: A278052 A093850 A297736 * A201740 A024212 A006408
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 10 2017
STATUS
approved