31815

Appears in sequences

• Numbers k such that sigma(k) = sigma(k+3).at n=3A015861
• Odd numbers k such that abs(sigma(k)-2k) <= sqrt(k). Abundance-radius = abs(sigma(k)-2k) does not exceed square root of k and k is odd.at n=15A087415
• Odd numbers n such that abs(sigma(n)-2n) <= n^(1/3). Abundance-radius = abs(sigma(n)-2n) does not exceed cubic root of n and n is odd.at n=5A088010
• Odd admirable numbers: such that sigma(n) = 2n + 2d for some d | n.at n=10A109729
• Admirable numbers such that the subtracted divisor is square.at n=14A109806
• Numbers k such that phi(k)=p^2, where p is product of digits of k.at n=8A153427
• Odd numbers whose abundancy is closer to 2 than any smaller odd number.at n=11A171929
• Odd abundant numbers whose abundancy is closer to 2 than any smaller odd abundant number.at n=5A188263
• Numbers k whose abundance is 18: sigma(k) - 2*k = 18.at n=3A223610
• Numbers k such that sigma(k) == 0 (mod k+9).at n=4A274563
• Irregular triangle read by rows where row n lists all odd primitive abundant numbers with n prime factors, counted with multiplicity.at n=39A287646
• Total number of elements (with multiplicity) in all subsets of [n] having a square element sum.at n=16A377572
• Expansion of e.g.f. (1/x) * Series_Reversion( x * exp(-arctanh(x)) ).at n=6A385501
• Odd numbers k that are closer to being perfect than previous terms and also satisfy the conditions that sigma(k) preserves the 3-adic valuation of k, and that sigma(k) == -k (mod 3).at n=8A386420
• Numbers k for which the symmetric representation of sigma, SRS(k), has at least 3 parts and all positive differences between two parts are at most 10, or all parts have the same size.at n=11A391474