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 A366606 Number of divisors of 4^n+1. 10
 2, 2, 2, 4, 2, 6, 4, 8, 2, 16, 4, 8, 8, 16, 4, 48, 4, 16, 16, 16, 4, 64, 8, 32, 8, 64, 8, 64, 8, 8, 16, 32, 4, 64, 12, 96, 32, 32, 16, 768, 8, 32, 32, 32, 16, 1536, 4, 16, 8, 64, 64, 512, 4, 16, 64, 96, 32, 256, 8, 128, 64, 64, 16, 1024, 4, 768, 128, 64, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Max Alekseyev, Table of n, a(n) for n = 0..561 FORMULA a(n) = sigma0(4^n+1) = A000005(A052539(n)). a(n) = A046798(2*n). - Max Alekseyev, Jan 08 2024 EXAMPLE a(3)=4 because 4^3+1 has divisors {1, 5, 13, 65}. MAPLE a:=n->numtheory[tau](4^n+1): seq(a(n), n=0..100); MATHEMATICA DivisorSigma[0, 4^Range[0, 100]+1] (* Paolo Xausa, Oct 14 2023 *) PROG (PARI) a(n) = numdiv(4^n+1); (Python) from sympy import divisor_count def A366606(n): return divisor_count((1<<(n<<1))+1) # Chai Wah Wu, Oct 14 2023 CROSSREFS Cf. A000005, A052539, A057940, A274903, A366602, A366605, A366607, A366608, A366609. Cf. A046798, A366577, A366616, A366628, A366637, A366656, A366665, A344897, A366688, A366714. Sequence in context: A054712 A345067 A066243 * A278242 A035580 A135293 Adjacent sequences: A366603 A366604 A366605 * A366607 A366608 A366609 KEYWORD nonn AUTHOR Sean A. Irvine, Oct 14 2023 STATUS approved

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Last modified August 9 16:51 EDT 2024. Contains 375044 sequences. (Running on oeis4.)