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 A140864 Smallest odd number with same number of divisors as 3*a(n-1). 2
 1, 3, 9, 15, 45, 105, 315, 945, 2835, 3465, 10395, 31185, 45045, 135135, 405405, 675675, 2027025, 3828825, 11486475, 34459425, 72747675, 218243025, 654729075, 1527701175, 4583103525, 11712375675, 35137127025, 105411381075 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Dimitri Papadopoulos, Table of n, a(n) for n = 1..56 EXAMPLE 9*3=27 has 4 divisors, but smallest odd number with 4 divisors is 15. PROG (PARI) a(nn) = {ia = 1; print1(ia, ", "); for (n = 1, nn - 1, nd = numdiv(3*ia); forstep(i = 1, 3*ia, 2, if (numdiv(i) == nd, ia = i; break; ); ); print1(ia, ", "); ); } \\ Michel Marcus, Jun 14 2013 (PARI) {/*prints b-file for A140864 - add more for loops for more terms*/ print("#A140864"); print(1" "1); print(2" "3); n = 3; for(p=3, 56, tau = numdiv(3*n); exp3n=factor(n)[1, 2]; delta = bigomega(exp3n+2) - bigomega(exp3n+1); delta = max(delta+1, 2); var = exp3n+delta; num = 10^1000; for( n1=1, var, for (n2=0, n1, for( n3=0, n2, for( n4=0, n3, for( n5=0, n4, for( n6=0, n5, for( n7=0, n6, for( n8=0, n7, for( n9=0, n8, for( n10=0, n9, for( n11=0, n10, for( n12=0, n11, for( n13=0, n12, for( n14=0, n13, for( n15=0, n14, if( (n1+1) * (n2+1) * (n3+1) * (n4+1) * (n5+1) * (n6+1) * (n7+1) * (n8+1) * (n9+1) * (n10+1) * (n11+1) * (n12+1) * (n13+1) * (n14+1) * (n15+1) == tau, numtemp = prime(2)^n1 * prime(3)^n2 * prime(4)^n3 * prime(5)^n4 * prime(6)^n5 * prime(7)^n6 * prime(8)^n7 * prime(9)^n8 * prime(10)^n9 * prime(11)^n10 * prime(12)^n11 * prime(13)^n12 * prime(14)^n13 * prime(15)^n14 * prime(16)^n15; if(numtemp < num, num = numtemp); )); ); ); ); ); ); ); ) ; ); ); ); ) ; ); ); ); print(p" "num); n=num; )} \\ Dimitri Papadopoulos, May 08 2019 CROSSREFS Cf. A053624, A019505. d(a(n)) = A036451(n) for first 18 terms. Sequence in context: A053624 A348198 A119239 * A171929 A188597 A330815 Adjacent sequences: A140861 A140862 A140863 * A140865 A140866 A140867 KEYWORD nonn AUTHOR J. Lowell, Jul 20 2008 EXTENSIONS a(10) through a(28) from Klaus Brockhaus, Jul 23 2008 a(29) through a(56) from Dimitri Papadopoulos, May 08 2019 STATUS approved

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Last modified February 4 10:27 EST 2023. Contains 360053 sequences. (Running on oeis4.)