A232689 G.f. A(x) satisfies: the sum of the coefficients of x^k, k=0..n, in A(x)^n equals 2^(n^2) for n>=0.

1, 1, 6, 150, 15684, 6626832, 11412679110, 80341130055678, 2305199459532741522, 268629428492391824756106, 126762373497858122449971372498, 241676422998164497873224935953948770, 1858392533076949187099229893507827126982592, 57560655711123829878000426546315591572901023820252

Offset: 0

Author

Paul D. Hanna, Dec 06 2013

Keywords

• nonn

Examples

			G.f.: A(x) = 1 + x + 6*x^2 + 150*x^3 + 15684*x^4 + 6626832*x^5 +...
ILLUSTRATION OF INITIAL TERMS.
If we form an array of coefficients of x^k in A(x)^n, n>=0, like so:
A^0: [1],0,  0,    0,      0,         0,            0,                0, ...;
A^1: [1, 1], 6,  150,  15684,   6626832,  11412679110,   80341130055678, ...;
A^2: [1, 2, 13], 312,  31704,  13286832,  22838822592,  160705169696760, ...;
A^3: [1, 3, 21,  487], 48078,  19980558,  34278483114,  241092139452066, ...;
A^4: [1, 4, 30,  676,  64825], 26708592,  45731714160,  321502059924816, ...;
A^5: [1, 5, 40,  880,  81965,  33471541], 57198570060,  401934951793740, ...;
A^6: [1, 6, 51, 1100,  99519,  40270038,  68679106021], 482390835814224, ...;
A^7: [1, 7, 63, 1337, 117509,  47104743,  80173378159,  562869732819493], ...; ...
then the sum of the coefficients of x^k, k=0..n, in A(x)^n (shown above in brackets) equals 2^(n^2):
2^0  = 1 = 1;
2^1  = 1 + 1 = 2;
2^4  = 1 + 2 + 13 = 16;
2^9  = 1 + 3 + 21 +  487 = 512;
2^16 = 1 + 4 + 30 +  676 + 64825 = 65536;
2^25 = 1 + 5 + 40 +  880 + 81965 + 33471541 = 33554432;
2^36 = 1 + 6 + 51 + 1100 + 99519 + 40270038 + 68679106021 = 68719476736; ...
		

Links

• Paul D. Hanna, Table of n, a(n) for n = 0..40

Crossrefs

Cf. A232687, A232606, A002416.

Programs

PARI

/* By Definition (slow): */
{a(n)=if(n==0, 1, (2^(n^2) - sum(k=0, n, polcoeff(sum(j=0, min(k, n-1), a(j)*x^j)^n + x*O(x^k), k)))/n)}
for(n=0, 20, print1(a(n)*1!, ", "))

PARI

/* Faster, using series reversion: */
{a(n)=local(B=sum(k=0, n+1, 2^(k^2)*x^k)+x^3*O(x^n), G=1+x*O(x^n));
for(i=1, n, G = 1 + intformal( (B-1)*G/x - B*G^2)); polcoeff(x/serreverse(x*G), n)}
for(n=0, 20, print1(a(n), ", "))

Formula

Given g.f. A(x), Sum_{k=0..n} [x^k] A(x)^n = 2^(n^2).