

A152677


Subsequence of odd terms in A000203 (sumofdivisors function sigma), in the order in which they occur and with repetitions.


5



1, 3, 7, 15, 13, 31, 39, 31, 63, 91, 57, 93, 127, 195, 121, 171, 217, 133, 255, 403, 363, 183, 399, 465, 403, 399, 511, 819, 307, 847, 549, 381, 855, 961, 741, 1209, 931, 1023, 553, 1651, 921, 781, 1815, 1281, 1143, 1093, 1767, 1953, 871, 2223, 2821, 993, 1995
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OFFSET

1,2


COMMENTS

Equivalently: subsequence of A000203 (sigma) with indices equal to a square or twice a square (A028982).
See A060657 for the set of odd values in the range of the sigma function, i.e., the list of odd values in ordered by increasing size and without repetitions.


LINKS

Table of n, a(n) for n=1..53.


FORMULA

a(n) = A000203(A028982(n)).  R. J. Mathar, Dec 12 2008


MATHEMATICA

Select[DivisorSigma[1, Range[1000]], OddQ[#] &] (* Giovanni Resta, Jan 08 2020 *)


PROG

(PARI) A152677_upto(lim)=apply(sigma, vecsort(concat(vector(sqrtint(lim\1), i, i^2), vector(sqrtint(lim\2), i, 2*i^2)))) \\ Gives [a(n) = sigma(k) with k = A028982(n) <= lim].  Charles R Greathouse IV, Feb 15 2013, corrected by M. F. Hasler, Jan 08 2020
(MAGMA) [d:k in [1..1000]IsOdd(d) where d is DivisorSigma(1, k)]; // Marius A. Burtea, Jan 09 2020


CROSSREFS

Cf. A000203 (sigma = sumofdivisors function), A152678 (even terms in A000203), A028982 (squares and twice the squares).
See A062700 and A023195 for the subsequence resp. subset of primes; A023194 for the indices of A000203 which yield these primes.
Sequence in context: A102032 A086517 A332374 * A135374 A253582 A117589
Adjacent sequences: A152674 A152675 A152676 * A152678 A152679 A152680


KEYWORD

easy,nonn


AUTHOR

Omar E. Pol, Dec 10 2008


EXTENSIONS

Extended by R. J. Mathar, Dec 12 2008
Edited and definition reworded by M. F. Hasler, Jan 08 2020


STATUS

approved



