A355941 Numbers k such that A003973(k) is a multiple of A000203(k).

1, 6, 14, 15, 24, 35, 42, 56, 105, 168, 210, 286, 376, 470, 552, 637, 672, 715, 840, 858, 874, 969, 1144, 1274, 1288, 1410, 1848, 1880, 2001, 2002, 2145, 2185, 2261, 2622, 3021, 3185, 3290, 3296, 3375, 3432, 3496, 3822, 4290, 4669, 4830, 4968, 5005, 5096, 5640, 6118, 6291, 6555, 6783, 7049, 7776, 8008, 9555, 9888

Offset

1,2

Comments

If both x and y are terms and gcd(x, y) = 1, then x*y is a term also.

Links

Table of n, a(n) for n=1..58.

Index entries for sequences computed from indices in prime factorization

Index entries for sequences related to sigma(n)

Mathematica

f[p_, e_] := ((q = NextPrime[p])^(e + 1) - 1)/(q - 1); Select[Range[10^4], # == 1 || Divisible[Times @@ f @@@ FactorInteger[#], DivisorSigma[1, #]] &] (* Amiram Eldar, Jul 22 2022 *)

Prog

(PARI)
A003973(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); sigma(factorback(f)); };
A355940(n) = !(A003973(n)%sigma(n));
isA355941(n) = A355940(n);

Crossrefs

Cf. A000203, A003973.

Positions of 1's in A355934, and also in A355940 (characteristic function).

Sequence in context: A107982 A341448 A081535 * A359912 A325698 A338907

Adjacent sequences: A355938 A355939 A355940 * A355942 A355943 A355944

Keyword

nonn

Author

Antti Karttunen, Jul 22 2022

Status

approved