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A376472
Composite terms in A376471.
2
6, 9, 20, 25, 77, 81, 121, 208, 256, 323, 361, 625, 667, 841, 1147, 1369, 1763, 1849, 2303, 2401, 3127, 3481, 4087, 4489, 5183, 5329, 6557, 6561, 6889, 8633, 9409, 10403, 10609, 11663, 11881, 14351, 14641, 16129, 17947, 18769, 20711, 22201, 23707, 24649, 27221
OFFSET
1,1
COMMENTS
Are there terms in this sequence that have more than 2 distinct prime factors?
LINKS
MATHEMATICA
expPow2Q[n_] := AllTrue[FactorInteger[n][[;; , 2]], # == 2^IntegerExponent[#, 2] &]; s[1] = 1; s[n_] := s[n] = Module[{prod = Times @@ Array[s, n - 1], k = s[n - 1] + 1}, While[! expPow2Q[prod*k], k++]; k]; Select[Array[s, 1000], CompositeQ]
PROG
(PARI) ispow2(n) = if(n == 0, 1, n >> valuation(n, 2) == 1);
lista(pindmax) = {my(pmax = prime(pindmax), v = vector(pindmax), f, pind, prd); for(k = 2, pmax, f = factor(k); pind = apply(x -> primepi(x), f[, 1]); for(i = 1, #pind, v[pind[i]] += f[i, 2]); if(vecprod(apply(x -> ispow2(x), v)) > 0, if(!isprime(k), print1(k, ", ")), for(i = 1, #pind, v[pind[i]] -= f[i, 2]))); }
CROSSREFS
Intersection of A002808 and A376471.
Sequence in context: A161782 A154783 A096546 * A357840 A355484 A358222
KEYWORD
nonn
AUTHOR
Amiram Eldar, Sep 24 2024
STATUS
approved