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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.
6
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).
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. A349169, A349752, A349755 (subsequences).
Sequence in context: A135054 A076701 A224773 * A076196 A330431 A349751
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 30 2021
STATUS
approved