A379224 The reversing binary representation of the sum of the divisors of the n-th odd square: a(n) = A065621(A379223(n)).

1, 21, 35, 73, 137, 397, 475, 695, 855, 901, 1837, 1657, 1301, 3277, 1451, 1057, 2881, 2859, 3971, 7135, 3023, 2477, 5099, 6513, 7953, 4283, 7539, 12335, 13801, 5757, 4939, 12049, 14969, 12885, 9277, 13321, 16175, 26873, 9893, 10705, 27281, 11589, 28533, 29775, 8671, 31171, 22197, 29287, 28519, 17253, 30787, 31337

Offset: 1

Author

Antti Karttunen, Dec 21 2024

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000
• Index entries for sequences related to binary expansion of n.
• Index entries for sequences related to sigma(n).

Crossrefs

The first column of square array A379221.

Cf. A065621, A379223.

Programs

Mathematica

A379224[n_] := BitXor[# - 1, 2*# - 1] & [DivisorSigma[1, (2*n - 1)^2]];
Array[A379224, 50] (* Paolo Xausa, Jan 23 2025 *)

PARI

A065621(n) = bitxor(n-1, n+n-1);
A379223(n) = sigma((2*n-1)^2);
A379224(n) = A065621(A379223(n));

Formula

a(n) = A065621(A379223(n)).