A351536 Odd numbers for which sigma(k) is congruent to 2 modulo 4 and the 3-adic valuations of k and sigma(k) are equal.

13, 37, 61, 73, 97, 109, 153, 157, 181, 193, 229, 241, 277, 313, 325, 337, 349, 373, 397, 409, 421, 433, 457, 541, 577, 601, 613, 661, 673, 709, 733, 757, 769, 801, 829, 853, 877, 925, 937, 997, 1009, 1021, 1033, 1069, 1093, 1117, 1129, 1153, 1201, 1213, 1237, 1249, 1297, 1321, 1381, 1429, 1453, 1489, 1525, 1549

Offset: 1

Author

Antti Karttunen, Feb 13 2022

Keywords

• nonn

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Intersection of A191218 and A349749. Cf. A349755 (subsequence).

Cf. A000203, A007949, A351534.

Programs

Mathematica

Select[Range[1, 1500, 2], Mod[(s = DivisorSigma[1, #]), 4] == 2 && Equal @@ IntegerExponent[{#, s}, 3] &] (* Amiram Eldar, Feb 13 2022 *)

PARI

isA351536(n) = if(!(n%2),0,my(s=sigma(n)); (2 == (s%4)) && (valuation(n,3) == valuation(s,3)));