A349749 Odd numbers k for which the 3-adic valuation of sigma(k) is equal to the 3-adic valuation of k, where sigma is the sum of divisors function.

1, 7, 13, 15, 19, 25, 31, 33, 37, 43, 61, 67, 69, 73, 79, 87, 91, 97, 103, 105, 109, 121, 123, 127, 133, 139, 141, 147, 151, 153, 157, 163, 175, 177, 181, 193, 195, 199, 211, 217, 223, 229, 231, 241, 247, 249, 259, 271, 277, 283, 285, 289, 301, 303, 307, 313, 325, 331, 337, 339, 343, 349, 367, 373, 375, 379, 393, 397

Offset

1,2

Comments

Odd numbers for which sigma (A000203) preserves the 3-adic valuation (A007949).

Links

Table of n, a(n) for n=1..68.

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Index entries for sequences related to sigma(n)

Mathematica

Select[Range[1, 400, 2], IntegerExponent[DivisorSigma[1, #], 3] == IntegerExponent[#, 3] &] (* Amiram Eldar, Dec 01 2021 *)

Prog

(PARI) isA349749(n) = ((n%2)&&valuation(sigma(n), 3)==valuation(n, 3));

Crossrefs

Cf. A000203, A007949, A329963, A349750, A349751.

Cf. A349169, A349752, A349755 (subsequences).

Sequence in context: A135054 A076701 A224773 * A076196 A330431 A349751

Adjacent sequences: A349746 A349747 A349748 * A349750 A349751 A349752

Keyword

nonn

Author

Antti Karttunen, Nov 30 2021

Status

approved