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 A226564 Numbers n such that sum(d|n, sigma(d)^2/d) is an integer, where d are the divisors of n. 5
 1, 205, 3895, 8525, 17050, 71951, 74005, 148010, 359755, 451825, 903650, 1628110, 1632005, 1798775, 2346674, 3597550, 4218285, 8436570, 8993875, 14749955, 17987750, 50471410, 59071771, 92802270, 95335075, 190670150, 280249145, 295358855, 451356495, 481068170 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Giovanni Resta, Table of n, a(n) for n = 1..34 (terms < 2*10^9) EXAMPLE Divisors of 71951 are 1, 11, 31, 211, 341, 2321, 6541, 71951. sigma(1) = 1, sigma(11) = 12, sigma(31) = 32, sigma(211) = 212, sigma(341) = 384, sigma(2321) = 2544, sigma(6541) = 6784, sigma(71951) = 81408. (1^2/1 + 12^2/11 + 32^2/31 + 212^2/211 + 384^2/341 + 2544^2/2321 + 6784^2/6541 + 81408^2/71951) = 102625. MAPLE with(numtheory); ListA226564:=proc(q) local a, b, k, n; for n from 1 to q do a:=[op(divisors(n))]; b:=add(sigma(a[k])^2/a[k], k=1..nops(a)); if type(b, integer) then print(n); fi; od; end: ListA226564(10^6); CROSSREFS Cf. A068978, A068986, A226563, A226564, A226566 Sequence in context: A203863 A203896 A203889 * A077457 A060892 A359498 Adjacent sequences: A226561 A226562 A226563 * A226565 A226566 A226567 KEYWORD nonn AUTHOR Paolo P. Lava, Jun 11 2013 EXTENSIONS a(12)-a(30) from Giovanni Resta, Jun 11 2013 STATUS approved

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Last modified April 13 15:06 EDT 2024. Contains 371644 sequences. (Running on oeis4.)