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 A229051 G.f.: Sum_{n>=0} (n^2)!/n!^n * (2*x)^n / (1-x)^(n^2+1). 2
 1, 3, 29, 13567, 1009142769, 19947560933879891, 170891375663413844489045533, 942542805274443250197129297402029958879, 4650425326497533656923054675764068523027405525255181377, 27202912617670436035808496756146798219927348043651854025145948950565355779 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..26 FORMULA a(n) = Sum_{k=0..n} 2^k * Product_{j=0..k-1} binomial(n+j*k,k). a(n) ~ exp(-1/12) * n^(n^2-n/2+1) * 2^n / (2*Pi)^((n-1)/2). - Vaclav Kotesovec, Sep 23 2013 EXAMPLE G.f.: A(x) = 1 + 3*x + 29*x^2 + 13567*x^3 + 1009142769*x^4 +... where A(x) = 1/(1-x) + (2*x)/(1-x)^2 + (4!/2!^2)*(2*x)^2/(1-x)^5 + (9!/3!^3)*(2*x)^3/(1-x)^10 + (16!/4!^4)*(2*x)^4/(1-x)^17 + (25!/5!^5)*(2*x)^5/(1-x)^26 +... Equivalently, A(x) = 1/(1-x) + (2*x)/(1-x)^2 + 6*(2*x)^2/(1-x)^5 + 1680*(2*x)^3/(1-x)^10 + 63063000*(2*x)^4/(1-x)^17 + 623360743125120*(2*x)^5/(1-x)^26 +...+ A034841(n)*(2*x)^n/(1-x)^(n^2+1) +... Illustrate formula a(n) = Sum_{k=0..n} 2^k * Product_{j=0..k-1} C(n+j*k,k) for initial terms: a(0) = 1; a(1) = 1 + 2*C(1,1); a(2) = 1 + 2*C(2,1) + 4*C(2,2)*C(4,2); a(3) = 1 + 2*C(3,1) + 4*C(3,2)*C(5,2) + 8*C(3,3)*C(6,3)*C(9,3); a(4) = 1 + 2*C(4,1) + 4*C(4,2)*C(6,2) + 8*C(4,3)*C(7,3)*C(10,3) + 16*C(4,4)*C(8,4)*C(12,4)*C(16,4); a(5) = 1 + 2*C(5,1) + 4*C(5,2)*C(7,2) + 8*C(5,3)*C(8,3)*C(11,3) + 16*C(5,4)*C(9,4)*C(13,4)*C(17,4) + 32*C(5,5)*C(10,5)*C(15,5)*C(20,5)*C(25,5); ... which numerically equals: a(0) = 1; a(1) = 1 + 2*1 = 3; a(2) = 1 + 2*2 + 4*1*6 = 29; a(3) = 1 + 2*3 + 4*3*10 + 8*1*20*84 = 13567; a(4) = 1 + 2*4 + 4*6*15 + 8*4*35*120 + 16*1*70*495*1820 = 1009142769; a(5) = 1 + 2*5 + 4*10*21 + 8*10*56*165 + 16*5*126*715*2380 + 32*1*252*3003*15504*53130 = 19947560933879891; ... MAPLE with(combinat): a:= n-> add(2^k*multinomial(n+(k-1)*k, n-k, k\$k), k=0..n): seq(a(n), n=0..10);  # Alois P. Heinz, Sep 23 2013 MATHEMATICA Table[Sum[2^k*Product[Binomial[n+j*k, k], {j, 0, k-1}], {k, 0, n}], {n, 0, 10}] (* Vaclav Kotesovec, Sep 23 2013 *) PROG (PARI) {a(n)=polcoeff(sum(m=0, n, (m^2)!/m!^m*(2*x)^m/(1-x+x*O(x^n))^(m^2+1)), n)} for(n=0, 15, print1(a(n), ", ")) (PARI) {a(n)=sum(k=0, n, 2^k*prod(j=0, k-1, binomial(n+j*k, k)))} for(n=0, 15, print1(a(n), ", ")) CROSSREFS Cf. A229050, A034841; A001850, A081798, A082488, A082489, A229049. Sequence in context: A213792 A133663 A270480 * A006526 A139517 A156026 Adjacent sequences:  A229048 A229049 A229050 * A229052 A229053 A229054 KEYWORD nonn AUTHOR Paul D. Hanna, Sep 22 2013 STATUS approved

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Last modified January 29 01:38 EST 2020. Contains 331328 sequences. (Running on oeis4.)