A009981 -id:A009981 - cp's OEIS frontend

A086874 Seventh power of odd primes.

2187, 78125, 823543, 19487171, 62748517, 410338673, 893871739, 3404825447, 17249876309, 27512614111, 94931877133, 194754273881, 271818611107, 506623120463, 1174711139837, 2488651484819, 3142742836021, 6060711605323

Offset: 1

Douglas Winston (douglas.winston(AT)srupc.com), Sep 16 2003

Cf. A000040, A001248, A030078, A030514, A050997, A030516, A000244, A000351, A000420, A001020, A001022, A001026, A001029, A009967, A009973, A009975, A009981, A009985, A009987, A009991.

Prime[Range[2,20]]^7 (* Harvey P. Dale, Sep 16 2013 *)

a(n) = prime(n+1)^7 \\ Michel Marcus, Jul 17 2013

A165858 Totally multiplicative sequence with a(p) = 37.

Original entry on oeis.org

1, 37, 37, 1369, 37, 1369, 37, 50653, 1369, 1369, 37, 50653, 37, 1369, 1369, 1874161, 37, 50653, 37, 50653, 1369, 1369, 37, 1874161, 1369, 1369, 50653, 50653, 37, 50653, 37, 69343957, 1369, 1369, 1369, 1874161, 37, 1369, 1369, 1874161, 37, 50653, 37

Offset: 1

Jaroslav Krizek, Sep 28 2009

G. C. Greubel, Table of n, a(n) for n = 1..10000

37^PrimeOmega[Range[50]] (* Harvey P. Dale, May 23 2014 *)

a(n) = 37^bigomega(n); \\ Altug Alkan, Apr 15 2016

a(n) = A009981(A001222(n)) = 37^bigomega(n) = 37^A001222(n).

A359059 Numbers k such that phi(k) + rad(k) + psi(k) is a multiple of 3.

Original entry on oeis.org

1, 2, 3, 5, 7, 8, 9, 11, 13, 17, 18, 19, 20, 23, 27, 29, 31, 32, 36, 37, 41, 42, 43, 44, 45, 47, 49, 50, 53, 54, 59, 61, 63, 67, 68, 71, 72, 73, 78, 79, 80, 81, 83, 84, 89, 90, 92, 97, 99, 101, 103, 105, 107, 108, 109, 110, 113, 114, 116, 117, 125, 126, 127, 128, 131, 135, 137, 139

Offset: 1

Torlach Rush, Dec 14 2022

nonn

When k is prime (denote as p), phi(p) = p - 1, rad(p) = p, and psi(p) = p + 1, so phi(p) + rad(p) + psi(p) = 3*p. Therefore, A000040 is a subsequence.

When k = p^m (m>=1) with p prime, phi(p^m) = (p-1)*p^(m-1), rad(p^m) = p, and psi(p^m) = (p+1)*p^(m-1), so phi(p^m) + rad(p^m) + psi(p^m) = 2*p^m + p = p * (1+2*p^(m-1)). Then, this expression is a multiple of 3 iff p == 0 or 1 (mod 3), equivalently iff p is a generalized cuban prime of A007645. Therefore, as 1 is also a term, every sequence {p^m, p in A007645, m>=0} is a subsequence. See crossrefs section. - Bernard Schott, Jan 25 2023 after an observation of Alois P. Heinz

			8 is a term because 4+2+12 is divisible by 3.

Cf. A000010 (phi), A000040, A001615 (psi), A007645, A007947 (rad), A001748 (3*p), A000244.

Subsequences of the form {p^n, n>=0}: A000244 (p=3), A000420 (p=7), A001022 (p=13), A001029 (p=19), A009975 (p=31), A009981 (p=37), A009987 (p=43).

q[n_] := Module[{f = FactorInteger[n], p, e}, p = f[[;; , 1]]; e = f[[;; , 2]]; Divisible[Times @@ ((p - 1)*p^(e - 1)) + Times @@ p + Times @@ ((p + 1)*p^(e - 1)), 3]]; Select[Range[170], q] (* Amiram Eldar, Dec 15 2022 *)

isok(m) = ((eulerphi(m) + factorback(factorint(m)[, 1]) + m*sumdiv(m, d, moebius(d)^2/d)) % 3) == 0; \\ Michel Marcus, Dec 27 2022

from sympy.ntheory.factor_ import totient
from sympy import primefactors, prod
def rad(n): return 1 if n < 2 else prod(primefactors(n))
def psi(n):
    plist = primefactors(n)
    return n*prod(p+1 for p in plist)//prod(plist)
# Output display terms.
for n in range(1,170):
    if(0 == (totient(n) + rad(n) + psi(n)) % 3):
        print(n, end = ", ")

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A086874 Seventh power of odd primes.

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A165858 Totally multiplicative sequence with a(p) = 37.

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A359059 Numbers k such that phi(k) + rad(k) + psi(k) is a multiple of 3.

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